<VjLjixf 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 

Class 


COMPOSITION    AND    HEAT 
TREATMENT    OF    STEEL 


Published   by  the 

McGraw-Hill    Book.  Company 

" 


to  theBookDepartments  of  tKe) 

McGra\v  Publishing  Company  xHill  Publishing  Company 

Publishers  of  Books  for 

Elec  trical  World  The  Engineering  and  Mining  Journal 

Engineering  Record  Power  and  The  Engineer 

Electric  Railway  Journal  American   Machinist 

Metallurgical  and  Qiemical  Engineering 


COMPOSITION   AND   HEAT 
TREATMENT    OF    STEEL 


BY 

E.   F.   LAKE 


SECOND  EDITION 

REVISED    AND    CORRECTED 


UNIVERSITY 

Of 

i&lfQKM 


McGRAW-HILL  BOOK  COMPANY 

239  WEST  39TH  STREET,  NEW  YORK 
6  BOUVERIE  STREET,  LONDON,  E.G. 

1911 


T 


MIMINU  o*rr. 

Copyright,  1910,  1911,  by  the  McGRAW-HiLL  BOOK  COMPANY 


PREFACE 

IN  preparing  the  matter  that  enters  into  this  book  no  attempt  has 
been  made  to  go  into  details  on  the  subjects  of  the  ores,  their  melting  down 
into  iron,  or  refining  the  iron  in  steel  making.  This  part  has  merely  been 
covered  in  a  general  way  in  order  to  lead  up  to  and  give  a  better  under- 
standing of  the  effect  of  the  elements  present  in  and  added  to  steels  of  the 
various  grades  and  kinds. 

An  attempt  has  been  made  to  cover  all  the  materials  that  have  been 
used,  either  commercially  or  experimentally,  for  the  purpose  of  making 
better  steel  and  improving  the  standard  brands  so  they  will  have  greater 
strengths;  withstand  strains  and  stresses  better;  possess  a  longer  wearing 
surface;  have  a  greater  electrical  resistance,  conductivity,  or  magnetism; 
attain  a  greater  hardness,  ductility,  resiliency,  or  malleability;  be  ca- 
pable of  taking  larger  cuts  on  other  metals  or  machining  them  faster;  pro- 
duce a  metal  that  can  be  easier  rolled,  hammered,  pressed,  drawn,  forged, 
welded,  or  machined  into  shape;  be  non-corrosive,  or,  in  fact,  make  a 
better  metal  for  any  of  the  many  uses  to  which  it  is  put.  The  effect  these 
materials  or  elements  have  had  upon  the  carbon  and  alloyed  steels  has  been 
told  as  well  as  the  data  at  hand  would  permit,  and  hints  have  been  in- 
jected, as  to  what  might  be  expected  from  many  of  the  elements,  in  order 
to  stimulate  further  investigations  and  experiments.  Results  have  been 
obtained  in  this  way  in  the  very  recent  past  that  are  truly  wonderful, 
yet  these  are  liable  to  sink  into  insignificance  before  the  discoveries  that 
may  be  made  in  the  near  future. 

The  different  chemical  compositions  that  can  be  made  from  the  ele- 
ments here  listed  and  described  are  so  numerous  that  it  seems  hopeless 
to  expect  that  all  of  them  will  ever  be  compounded,  and  tests  made,  and 
the  results  recorded.  However,  with  the  many  individuals  that  are 
working  along  these  lines  some  combinations  are  bound  to  be  made  that 
will  prove  to  be  beneficial,  and  doubtless  some  steels  will  be  produced  that 
will  cause  as  great  a  revolution  as  "Mushet"  or  " Bessemer"  steels  did  in 
their  respective  lines.  A  very  few  of  the  possible  quaternary  steels 
have  been  tried,  i.e.,  alloys  made  by  combining  four  different  elements 
with  the  ferrite,  and  therefore  many  are  yet  to  be  investigated  in  the  many 
different  percentages  in  which  it  is  possible  to  combine  them.  And  this 
does  not  take  into  consideration  the  compositions  that  are  possible  with 
six,  eight  or  more  elements. 


212108 


vi  PREFACE 

Following  the  ingredients  of  and  materials  used  in  steel,  comes  the 
heat-treatment,  as  the  two  have  moved  along  parallel  lines,  in  the  many 
investigations,  experiments,  and  improvements  that  have  been  made, 
and  seem  to  be  inseparable.  Each  change  in  composition  seems  to  have 
altered  the  heat-treatment,  and  each  improvement  in  heat-treatment  seem 
to  have  altered  the  percentage,  that  is  best  to  use,  of  some  one  or  more 
element.  Many  different  methods  and  various  kinds  of  materials  have 
been  experimented  with  and  consequently  a  great  deal  of  useful  informa- 
tion has  been  obtained  and  many  improvements  of  a  radical  nature  made. 
New  methods,  new  materials,  and  new  apparatus  have  thus  been  brought 
into  use  for  the  heat-treatment  of  steel.  These  have  enabled  the  hardener 
to  get  more  definite,  positive,  and  uniform  results,  and  in  this  way  the  metal 
has  been  improved  to  a  great  extent. 

All  of  the  information  that  could  be  obtained  on  this  phase  of  steel 
making  and  working  has  therefore  been  recorded  as  carefully  as  possible. 
This  also  suggests  ideas  that  would  indicate  that  there  is  still  room  for 
important  improvements  or  discoveries.  One  of  these  is  the  attaching 
of  a  positive  and  negative  wire  of  an  electrical  circuit  to  the  piece  of  steel 
to  be  hardened  and  place  it  in  a  quenching  bath.  The  current  can  then 
be  turned  on,  the  piece  heated,  the  current  turned  off,  and  the  piece 
quenched  without  moving  it  or  allowing  the  air  to  strike  the  metal  and  oxi- 
dize it.  Another  instance  is  the  possibilities  suggested  by  carbonizing 
steel  with  gases  or  chemicals  and  thus  doing  away  with  the  old  laborious 
method  of  packing  the  steel  pieces  in  bone  and  charcoal.  Still  another 
is  the  30-minute  annealing  of  high  speed  steel  and  the  possibility  of  a 
similar  method  being  applied  to  carbon  steel. 

In  gathering  together  the  data  necessary  to  add  to  my  own,  very  little 
credit  has  been  given  to  individuals,  as  to  make  this  correct  is  not  only 
a  laborious  but  a  hopelessly  impossible  task.  To  illustrate  this  I  have 
seen  professors  claim  as  their  own  discoveries,  new  principles,  new  methods, 
etc.,  that  were  developed  and  perfected  by  students  in  their  classes,  and 
shop  foremen  and  superintendents  claim  as  theirs,  inventions  made  by 
men  in  the  shop.  Two  important  discoveries  that  developed  into  new 
kinds  of  steel  were  made  through  the  mistakes  of  workmen  in  steel 
mills.  Two  men  on  the  same  job  added  the  correct  percentage  of  a 
material  and  thus  this  element  was  twice  as  large  as  it  was  thought 
would  give  good  results.  In  fact,  it  was  believed  that  it  would  injure 
the  metal  to  add  more  than  a  certain  percentage,  but  when  this  maxi- 
mum percentage  was  doubled  the  metal  was  given  properties  that  were 
very  beneficial  for  certain  purposes.  None  of  us  can  add  but  a  mite  to 
the  knowledge  that  we  have  obtained  from  others  and  because  we  are 
enabled  to  write  it  so  it  will  be  recorded  in  books  and  papers  does  not 
give  us  the  privilege  of  claiming  to  be  the  originators  of  certain  ideas, 


PREFACE  vii 

principles,  discoveries,  or  inventions.  Every  one  who  has  worked  in  the 
steel  mill  or  the  laboratory  is  entitled  to  a  part  of  the  credit  for  any  new 
ideas  or  information  that  may  happen  to  be  enclosed  between  the  two 
covers  of  this  book.  To  pick  out  a  few  individuals  and  give  less  credit 
than  this  would  be  working  an  injustice  and  stating  an  untruth,  and  to 
name  all  that  should  be  given  credit  is  a  physical  impossibility. 

E.  F.  LAKE. 


CONTENTS 

CHAPTER  PAGE 

I    THE  MAKING  OF  PIG  IRON 1-12 

Ordinary  blast  furnace  reduction  of  ores,  1-3;  Use  of  excess  gas,  4;  Con- 
veying molten  metal  in  ladle  cars,  5;  Making  pig  beds  in  sand  floor,  6; 
Casting  pigs  in  iron  molds,  7-8;  Electric  blast  furnace,  9-12. 

II    BESSEMER  PROCESS  OF  CONVERTING  IRON  INTO  STEEL 13-21 

Burning  out  impurities,  13;  Recarburizing,  14-15;  Casting  into  ingots, 
16;  Acid  and  basic  Bessemer  process,  17;  Metal  for  ingot  molds,  18;  Steel 
rails,  19. 

III  OPEN-HEARTH  PROCESS  FOR  MAKING  STEEL 22-33 

Stationary  and  tilting  furnaces,  22-27;  Charging  machine,  28;  Acid 
open-hearth  furnace,  29;  Basic  open-hearth  furnace,  30-31;  Other  open- 
hearth  processes,  32;  Fluid  ingot  compressor,  33. 

IV  CRUCIBLE  PROCESS  OF  STEEL  MAKING      .     .     .     .  3  .     .     .     .     ;     •  34-41 

Kind  of  crucibles  used,  34;  Regenerative  furnace,  35;  Charging  crucibles, 
36;  Pouring  ingots,  37;  Hammering  ingots,  38;  Making  into  bars,  39; 
Wrought  iron,  40-41. 

V    ELECTRIC  FURNACES  FOR  STEEL  MAKING 42-63 

Stassano  revolving  furnace,  42-43;  Heroult  furnace,  44-47;  Keller  fur- 
nace, 47-48;  Kjellin  and  Colby  furnaces,  49-53;  Rochling-Rodenhauser 
furnace,  53-56;  Girod  furnace,  56-61;  Summary,  61-63. 

VI     INGREDIENTS  OF  AND  MATERIALS  USED  IN  STEEL 64-110 

Carbon,  64-71;  Manganese,  71-75;  Silicon,  75-77;  Phosphorus,  78-80; 
Sulphur,  80-83;  Oxygen,  Hydrogen,  and  Nitrogen,  83-86;  Copper,  &6-8S; 
Arsenic,  Antimony,  and  Bismuth,  88-90;  Boron,  91-93;  Tantalum,  93; 
Platinum,  94;  Nickel,  95-97;  Cobalt,  97-98;  Chromium,  99-100;  Tungsten, 
100-102;  Molybdenum,  102-103;  Vanadium,  103-105;  Titanium,  105-108; 
Aluminum,  109;  Tin,  109;  Yttrium,  110;  Cerium  and  Lanthanum,  110. 

VII    WORKING  STEEL  INTO  SHAPE 111-150 

Rolling,  111-115;  Rules  for  rolling,  115;  Temperatures,  116;  Apparatus  for 
melting  metal  for  castings,  116-117;  Risers,  gates,  etc.,  117-118;  Composi- 
tion of  steel  castings,  118-119;  Vanadium  steel  castings,  119-120;  Titanium, 
120;  Nickel-steel  castings,  120;  Direct-steel  castings,  121;  Manganese-steel 
castings,  121;  Chrome-steel  castings,  122;  Forgeability  of  different  steels, 
123-124;  Effect  of  temperature  on  the  grain,  124-126;  Hand-forging,  126; 
Steam-hammer  forging,  127-130;  Drop-hammer  forging,  131-135;  Pressed 
forgings,  135-143;  Welding,  143-145;  Electric  welding,  145-147;  Welding 
with  gases,  147-149;  Thermit  welding,  149-150. 

VIII    FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT      .     .     .     .     .    151-184 

Theory  of  heat-treatment,  151-152;  Hard-fuel  furnace,  153;  Liquid  fuel, 
154-156;  Oil  burner,  156;  Over-fired  furnace,  157-159;  Under-fired  furnace, 

ix 


x  CONTENTS 

CHAPTER  PAGE 

160-162;  Water-jacketed  front,  162;  Gaseous  fuel,  163;  Oven  furnace,  164; 
Revolving  retort  and  upright  furnaces,  165;  Automatic  furnaces,  166^169; 
Gas-booster,  170;  Automatic  temperature  control  for  furnaces,  170-173; 
Heating  in  liquids,  174;  Lead-bath  furnace,  175-176;  Cyanide  of  potassium 
furnace,  177;  Barium-chloride  furnace,  178-181;  Electric  furnaces,  182-184. 

IX    ANNEALING  STEEL     ' .    -  *     .     .     . 185-191 

Theory  and  methods,  185-186;  Rules  for  hammered  stock,  187;  Laws 
on  annealing,  188-189;  Apparatus  for  annealing,  190-191. 

X     HARDENING  STEEL      .      .      .      .      .      .      . '  " .      .    192-213 

Theory,  192;  Microscopical  examination,  193;  Ferrite,  193;  Cementite, 
193;  Pearlite,  194;  Martensite  and  Hardenite,  195;  Sorbite,  195;  Austenite, 
195-196;  Troostite,  197;  Effect  of  composition  and  hardening,  197-199; 
Baths  for  hardening,  199-202;  Methods  of  keeping  bath  cool,  202-204; 
Electrical  hardening,  204-205;  Cracking  and  warping,  205-208;  High- 
speed steel,  208-209;  Hardening  furnaces,  210-213. 

XI    TEMPERING  STEEL .  .  „••' ..-.'-   t     .   214-226 

Negative  and  positive  quenching,  214;  Temperatures  at  which  to  draw 
tools,  215-216;  Failures  when  tempering  by  color,  216-217;  Effect  of 
tempering  on  springs,  218-219;  Effect  on  strength  of  steel,  220;  Mixtures 
of  lead  and  tin  for  tempering  baths,  223;  Tempering  furnaces  and  baths, 
220-226. 

XII    CARBONIZING 227-246 

Different  kinds  of  carbonizing,  227-228;  Factors  governing  carbonizing, 
228-230;  Carbonizing  materials,  231-232;  Results  obtained  with  gases, 
233-234;  Speed  of  penetration,  234r235;  Effect  of  temperature,  236; 
Heat-treatment  after  carbonizing,  236-237;  Time  of  exposure,  237-238; 
Carbonizing  with  gas,  238-245;  Local  hardening,  245-246. 


TH€ 

UNIVERSITY 

Of 

LUFORH\J 


COMPOSITION  AND  HEAT  TREATMENT  OF  STEEL 

CHAPTER  I 
THE  MAKING  OF  PIG  IRON 

THE  iron  that  forms  the  base  for  all  steel,  as  well  as  iron,  products  is 
first  obtained  from  its  ores,  as  a  commercial  product,  from  a  blast  furnace 
similar  to  that  shown  in  Fig.  1.  It  is  then  in  the  form  of  an  iron  that 
contains  a  large  amount  of  carbon,  both  in  the  graphitic  and  combined 
state.  This  makes  it  too  weak  and  brittle  for  most  engineering  purposes, 
but  about  one-third  of  the  total  product  is  run  out  of  the  blast  furnace 
into  pigs  of  iron  that  is  used  only  for  castings  that  are  to  be  subjected 
to  compressive,  transverse  or  very  slight  tensile  strains,  such  as  bed 
plates  or  supporting  parts  for  machinery,  stove  plates,  car  wheels,  etc. 

The  various  kinds  of  steels  are  relatively  increasing  in  proportion 
to  the  amount  of  pig  iron  used.  To-day  about  two-thirds  of  this 
product  is  being  turned  into  steel  through  purification  by  either  the 
Bessemer,  open-hearth,  puddling,  crucible,  or  electric  methods.  The 
carbon  content  is  reduced  to  any  desired  point,  the  graphitic  carbon 
being  eliminated  by  any  of  these  processes,  and  the  silicon  and  man- 
ganese are  oxidized  out  by  the  accompanying  reactions,  or  as  a  condition 
precedent  to  the  reduction  of  the  carbon.  The  two  impurities  of  the 
metal  which  are  the  greatest  bane  to  engineers  and  steel  makers  alike 
are  phosphorus  and  sulphur.  These  are  reduced  by  either  the  basic 
open-hearth,  puddling,  or  electric  processes. 

In  making  steel,  the  operation  begins  by  making  pig  iron  from  the 
iron  ore,  which  is  a  natural  iron  rust  or  a  combination  of  iron  and  oxygen. 
The  oxygen  is  removed  by  combining  iron  ore,  coke,  and  limestone  in  a 
furnace,  as  shown  in  Fig.  2,  and  heating  them  to  a  high  temperature  by 
injecting  superheated  air  into  the  bottom  of  the  furnace.  The  coke  is 
burned  by  the  oxygen  in  the  air;  a  part  of  it  aids  in  maintaining  this 
high  temperature  while  the  rest  is  useful  in  removing  the  oxygen. 

This  superheated  air  is  usually  produced  by  passing  the  blast  through 
a  hot  blast  stove.  This  has  been  previously  heated  by  means  of  the  com- 
bustible gases  which  have  been  conducted  from  the  top  of  the  furnace  to 
the  bottom  through  the  pipe  shown  to  the  left  of  the  furnace  in  Fig.  2. 

Four  of  these  stoves  are  shown  grouped  in  pairs,  to  the  left  of  the 
blast  furnace,  in  Fig.  1.  They  are  about  the  same  height  as  the  furnace, 

1 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


THE   MAKING  OF  PIG  IRON 


Coke 

IP  Iron  Ore 

O  Lime 

u  Drops  of  Slag 

•  Drops  of  Iron 

:~-~3J:l  Molten  Slag 

ff^QC  Molten  Iron 


FIG.  2.  —  Details  of  blast  furnace.    Condition  of  charge  at  different 

levels. 


4  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

which  may  be  from  60  to  100  feet,  and  are  round  steel  tanks  that  have  a 
comparatively  small  annular  fire-brick  chamber  in  the  center  for  nearly 
the  height  of  the  tank.  This  chamber  is  surrounded  with  brick  work  that 
is  filled  with  flues.  The  gas  from  the  furnace  comes  in  at  the  bottom  of 
the  central  annular  chamber;  burns  on  its  passage  up  this;  comes  down 
through  the  flues  in  a  heated  condition,  thus  heating  up  the  brick  work, 
and  then  passes  out  the  chimney  as  waste  product. 

When  the  brick  work  is  heated  properly,  the  gas  from  the  furnace  is 
shut  off  and  the  air  blast  from  the  blowing  engines  passed  through  the 
stove  on  its  way  to  the  furnace. 

This  heats  the  air  in  its  passage  up  through  the  central  chamber  and 
down  through  the  flues,  and  makes  it  a  hot  blast  when  it  enters  the  tuy- 
eres of  the  furnace.  Thus  it  increases  the  temperature  of  combustion  in 
the  blast  furnace.  Four  hot  blast  stoves  are  used  with  each  furnace,  so 
that  three  can  be  burning  gas  and  warming  up,  while  the  fourth  is  having 
the  air  blast  sent  through  it  into  the  furnace. 

The  gas,  which  is  a  product  of  combustion  of  the  materials  in  the 
blast  furnace,  comes  down  through  the  pipe  A  (Fig.  2),  which  is  called 
the  downcomer,  leaves  most  all  of  its  accumulated  dirt  at  B,  and  then 
passes  out  of  the  pipe  C. 

From  one-third  to  one-half  of  this  gas  is  all  that  is  needed  to  keep  the 
stoves  hot  and  the  balance  is  generally  burnt  under  the  boilers  where  it 
generates  the  steam  for  the  blowing  engines.  In  some  cases  it  is  used 
directly  in  gas  blowing  engines.  Often  there  is  more  than  enough  gas 
for  the  heat  and  power  requirements  of  the  blast  furnace  and  the  excess 
is  used  to  generate  a  part  of  the  power  used  by  the  steel  mills. 

The  blast  furnace  is  usually  charged  by  means  of  a  skip  car  running 
on  an  inclined  track.  The  charge  is  dumped  from  the  car  into  the  top  of 
the  furnace  through  a  hopper  and  bell,  and  consists  of  coke,  iron  ore  and 
limestone.  The  change  that  takes  place  in  these  as  they  pass  down  through 
the  furnace  is  plainly  shown  in  Fig.  2. 

The  coke  serves  as  a  fuel  for  generating  the  heat  that  melts  the  iron 
ore,  and  the  limestone  unites  with  the  earthy  material  as  the  ore  is  being 
reduced  to  a  molten  state.  The  resultant  slag  is  run  off  from  the  top  of 
the  iron  through  a  hole  in  the  side  of  the  furnace  below  the  tuyeres.  The 
metallic  iron  melts  and  collects  in  the  hearth  below  this  slag,  and  is  tapped 
out  of  another  hole,  close  to  the  bottom.  From  this  it  is  run  through 
channels  into  molds  that  form  it  into  "sows"  and  "pigs,"  or  the  molten 
metal  is  tapped  from  the  furnace  into  ladle  cars  as  shown  in  Fig.  3,  in 
which  it  is  taken  to  furnaces  for  conversion  into  steel. 

While  the  metal  is  in  contact  with  the  white-hot  coke  in  the  furnace 
it  absorbs  a  certain  amount  of  carbon,  some  of  which  is  chemically  com- 
bined with  the  iron  and  another  part  is  held  in  suspension  as  graphite. 


THE  MAKING  OF  PIG  IRON 


6 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


If  the  "sows"  and  "pigs"  are  cooled  slowly  it  tends  to  make  the  carbon 
take  the  form  of  graphite.  When  such  iron  is  broken  it  has  a  gray  or 
black  appearance  showing  loose  scales  of  graphite,  and  the  iron  is  soft 
and  tough. 

If  the  metal  is  cooled  quickly,  or  chilled  as  soon  as  it  comes  from  the 
furnace,  the  carbon  has  a  tendency  to  be  kept  in  the  combined  state. 
When  fractured  such  metal  will  be  white  and  hard. 

Of  this  product  about  20%  is  made  into  gray-iron  castings,  3%  into 
malleable-iron  castings,  3%  is  purified  in  puddling  furnaces  to  make 
wrought  iron,  and  the  balance,  or  74%,  is  converted  into  steel  by  the  various 


Skimmer  • 


Sow  M 

MOT 


I 


w 


FIG.  4.  —  Section  of  sand  bed  for  cast- 
ing pig  iron. 

processes.  Of  the  latter  about  40%  is  converted  by  the  Bessemer  process, 
31%  in  the  basic  open-hearth  furnace,  and  3%  in  the  acid  open-hearth 
furnace. 

About  6%  of  the  production  of  wrought  iron  goes  into  the  manufac- 
ture of  crucible  steel.  Recently  the  electric  furnace  has  been  brought 
into  use,  and  this  promises  to  take  a  certain  percentage  for  conversion  into 
the  finer  grades  of  steel. 

The  older  method  of  casting  the  blast  into  pigs,  and  which  is  still  used 
now  by  many  is  to  have  a  casting  floor  in  front  of  the  blast  furnace  that 
is  composed  of  silica  sand.  In  this  sand,  impressions  or  molds  are  made 
for  the  pigs  and  these  connected  with  runners  called  "sows,"  which  in 
turn  are  connected  to  a  main  runner  from  the  furnace.  Fig.  4  shows  how 


THE  MAKING  OF  PIG  IRON  7 

the  floor  is  laid  out.  In  front  of  and  under  the  tap  hole  of  the  furnace  a 
trough  is  laid  into  which  the  iron  is  run.  From  this  the  main  runner  for 
the  iron  goes  down  the  center  of  the  cast-house.  Branching  off  on  either 
side  of  this  are  the  sows  with  the  pigs  leading  off  from  the  sows. 

Removable  dams  are  formed  at  the  junction  of  each  sow  with  the  main 
runner.  .  The  iron  is  first  allowed  to  flow  into  the  sow  and  pigs  at  the  lower 
end  of  the  runner,  i.e.,  at  that  end  farthest  from  the  furnace.  When  these 
are  filled  the  iron  is  dammed  off  by  thrusting  a  " cutter"  into  the  runner 
just  below  its  junction  with  the  next  higher  sow,  the  dam  at  the  entrance 
of  the  sow  being  at  the  same  time  broken  so  that  the  iron  can  enter.  This 
is  continued  with  successively  higher  sows  and  rows  of  pig  beds  until 
all  of  the  iron  has  run  out  of  the  furnace.  After  solidifying  and  cooling 
the  pigs,  sows  and  runner  are  broke  up,  loaded  on  cars  and  the  floor 
remolded,  ready  for  the  next  tapping.  At  the  entrace  to  each  pig  and  at 
stated  intervals  in  the  sows  and  runner,  as  shown  by  the  double  lines, 
a  dam  is  formed  that  about  half  filled  these,  so  as  to  make  the  metal 
thinner  at  this  point  and  thus  allow  it  to  be  broken  more  easily  into  nearly 
standard  sizes  and  weights. 

Automatic  machines  into  which  the  pigs  are  cast,  cooled,  and  then 
dumped  into  cars  are  now  used  at  some  blast  furnaces,  as  the  saving  in 
labor  is  a  big  item;  the  pigs  are  more  uniform  in  size,  thus  facilitating 
handling,  piling,  and  storing,  and  they  are  free  from  the  adhering  silicious 
sand  that  is  especially  objectionable  in  the  basic  open-hearth  furnace. 

The  pig  molding  machines  are  made  in  several  styles,  the  most 
common  forms  of  which  are  a  revolving  frame  with  the  pig  molds  in  a 
continuous  series  around  its  annular  outer  edge,  as  shown  in  Fig.  5,  and  a 
series  of  molds  attached  to  an  endless  chain  which  carries  them  in  a  straight 
line  from  where  they  are  poured  to  the  cars  into  which  they  are  dumped, 
as  shown  in  Fig  5.  In  the  latter,  the  empty  molds  travel  back  to  the 
ladle  underneath  the  filled  ones,  and  in  both  the  molds  are  sprayed  with 
thick*  lime  water,  long  enough  before  they  are  filled  to  allow  the  water 
to  be  dried  out  by  the  heat  of  the  mold,  and  leave  it  covered  with  a  coat- 
ing of  lime  so  the  molten  metal  will  not  stick  to  the  steel  molds. 

ELECTRIC   SMELTING    FURNACE 

The  experiments  that  have  for  some  time  been  carried  on  for  the 
electric  production  of  pig  iron  seem  to  be  fast  approaching  a  successful 
culmination,  and  we  may  in  the  near  future  see  this  method  used  com- 
mercially, especially  where  an  adequate  water  power  is  available. 

The  Noble  Steel  Company  in  California  have  built  several  furnaces 
in  this  country.  Their  first  attempt  was  a  1500  kilowatt,  three-phase, 
resistance  type  of  furnace  that  was  completed  in  July,  1907,  but  after 
running  it  a  short  time  the  mechanical  difficulties  which  presented  them- 


8 


COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 


THE   MAKING   OF   PIG  IRON 


9 


selves  made  this  type  of  furnace  impractical  commercially,  and  it  was 
abandoned. 

A  160  kilowatt  furnace  of  a  different  type  was  then  constructed  and 
run  for  40  days.  From  this  run  data  were  gathered  that  were  used  in 
the  construction  of  the  present  1500  kilowatt  furnace,  shown  in  Fig.  7. 
The  data  obtained  would  indicate  that  with  one  ton  of  charcoal,  costing 
about  $9,  three  tons  of  pig  iron  could  be  produced  with  about  0.25 
electric  horse-power-year  per  ton. 

The  quantity  of  carbon  used  for  the  electric  smelting  of  iron  ores  is 
only  about  one-third  of  that  required  for  the  ordinary  blast  furnace. 


FIG.  6.  —  Double  strand,  endless  chain,  pig  casting  machine. 

Thus  charcoal  can  be  used  and  the  product  will  be  charcoal  pig  iron, 
which,  owing  to  its  comparative  purity,  would  demand  a  higher  price 
than  the  ordinary  product. 

In  the  furnace  shown  in  Fig.  7,  the  ore  with  its  proper  fluxing  materials 
is  brought  in,  in  cars,  and  fed  into  the  preheater,  A,  where  it  is  dried  and 
heated  by  the  products  of  combustion  piped  from  the  combustion  cham- 
ber of  the  furnace,  B,  through  the  flue,  C.  After  drying  it  is  dumped 
in  the  scale  car,  D,  which  runs  around  the  top  of  the  stack,  on  a  circular 
track,  so  it  can  alternately  take  a  charge  of  ore  and  flux  from  A,  and 
carbon  from  the  hopper,  E,  weigh  them  and  charge  them  into  the  furnace 
in  the  proper  proportions  through  the  usual  hopper  and  bell  in  the  top 
of  the  stack. 


10 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


Six  electrodes  (<•?)  are  arranged  equidistantly  around  the  furnace, 
and  the  electric  current  passing  through  between  them  melts  the  charge, 
the  metal  and  slag  collecting  in  the  crucible  at  the  bottom  of  the  furnace, 
from  which  they  are  drawn  as  in  ordinary  practice.  All  the  necessary 
heat  is  supplied  by  electrical  energy,  and  thus  no  blast  is  blown  in.  This 
causes  all  of  the  solid  carbon  to  be  used  for  reduction,  excepting  of  course 
the  small  amount  that  is  dissolved  into  the  pig  iron.  Above  the  level 
of  the  charge,  however,  are  small  openings  at  F,  for  admitting  the  correct 


FIG.  7.  —  Electric  pig-iron  furnace  at  Noble  Steel 
Co.,  Heroult,  Cal. 

amount  of  air,  through  valves,  to  burn  the  gases  that  result  from  the 
reduction  of  the  ores  in  the  lower  part  of  the  furnace. 

In  Fig.  8  is  shown  the  combination  of  electric  and  blast  furnace  that 
has  resulted  from  several  years  of  study  and  experiments  conducted  by 
three  Swedish  engineers  at  the  Domnarfvet  Iron  Works  in  Sweden.  In 
this  a  large  crucible  with  an  arched  roof  is  formed  at  /.  An  opening  is 
left  in  the  center  of  the  roof,  and  over  it  is  constructed  a  stack  (J)  very 
similar  to  the  ordinary  blast  furnace;  in  fact,  the  only  difference  being 
that  the  bosh  is  contracted  more  at  K,  where  the  charge  enters  the  crucible. 
This  was  made  necessary  by  the  fact  that  too  large  an  opening  would 
not  retain  the  required  heat  in  the  crucible  part  of  the  furnace  without 


THE  MAKING  OF  PIG  IRON 


11 


increasing  the  power  to  generate  the  electrical  energy  to  too  high  a  point. 
It  was  feared  that  this  contraction  would  result  in  the  furnace  clogging 


FIG.  8.  —  Electric  furnace  at  Domnarfvet  Iron  Works,  Sweden. 

and  an  overhang  form  in  the  bosh,  but  with  a  continuous  run  of  three 
months  no  such  condition  was  apparent. 

Three  electrodes  (L)  that  project  into  the  crucible  through  a  water- 


12  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

jacketed  stuffing-box  in  the  arched  roof  conduct  a  three-phase  alternating 
current  of  40  volts  to  the  charge.  The  current  is  from  8000  to  9500 
amperes,  and  the  load  480  to  500  kilowatts.  The  arched  roof  over  the 
crucible  gave  considerable  trouble  in  the  earlier  experiments  by  being 
overheated,  but  this  is  now  preserved  by  taking  the  gaseous  products  of 
combustion  from  the  top  of  the  furnace  at  M,  and  blowing  them  back 
through  tuyeres  at  N,  which  are  provided  with  peep-holes  so  the  roof 
can  be  examined  and  the  volume  of  gas  increased  or  diminished  as  desired. 

In  the  three  months'  run,  that  was  terminated  July  3,  1909,  by  the 
general  strike  in  Sweden,  it  was  demonstrated  that  the  electrodes  did 
not  need  readjusting  oftener  than  once  a  day,  and  in  one  case  an  electrode 
was  not  touched  for  five  days;  that  the  consumption  of  energy  was 
remarkably  uniform  even  though  the  short  run  did  not  enable  the 
furnace  to  approach  its  working  condition  until  near  the  end;  that  the 
charge  moved  with  regularity  into  the  melting  chamber;  free  spaces  were 
maintained  underneath  the  arched  roof  next  to  the  outer  wall,  and  the 
gases  kept  the  roof  effectively  cooled. 

This  furnace  was  first  constructed  as  an  induction,  but  was  later 
changed  to  a  resistance  furnace.  It  is  started  and  worked  the  same  as 
the  ordinary  blast  furnace,  and  in  the  experiments  so  far  only  coke  has 
been  used,  but  charcoal  can  be  used  as  well  as  the  " prime  ore  briquettes" 
and  "slig"  which  they  get  in  Sweden.  It  has  produced  2  tons  of  iron 
per  electrical  horse-power-year,  but  conditions  would  indicate  that  this 
could  be  increased  to  3  tons.  It  being  easy  to  make  a  pig  iron  in  this 
furnace  with  a  low  carbon  content,  if  the  molten  iron  was  transferred 
directly  to  electric  refining  furnaces,  it  would  greatly  reduce  the  time 
consumed  in  converting  it  into  steel.  It  now  takes  a  comparatively  long 
time  to  reduce  the  carbon  to  the  percentage  required  in  the  electric  con- 
verting furnace  when  ordinary  blast-furnace  iron  is  used. 

The  carbon  in  the  experiments  with  the  Swedish  furnace  averaged 
about  1.80%  in  the  three  months'  run,  while  in  some  previous  experi- 
ments it  ran  as  high  as  3.20%,  and  in  one  tapping  it  was  as  low  as  1%. 
The  silicon  varied  between  0.20  and  0.07%,  but  in  one  case  was  4.40%. 
The  sulphur  content  has  been  as  low  as  0.005%,  with  0.50%  of  sulphur 
in  the  coke  that  was  used. 

The  ability  of  the  electric  furnace  to  reduce  the  impurities  to  a  mini- 
mum may  result  in  its  becoming  a  prominent  factor  in  the  reduction 
of  the  ore,  and  the  conversion  of  this  into  steel  as  soon  as  experience 
teaches  the  operators  to  control  the  carbon  and  silicon,  and  it  is  demon- 
strated that  it  is  practical  commercially.  In  Denmark  there  will  soon 
be  started  another  ore  furnace,  and  in  Canada  negotiations  are  well 
advanced  for  an  electric  iron-ore  reduction  and  steel  plant  with  a  capacity 
of  5000  horse-power. 


CHAPTER  II 
BESSEMER  PROCESS  OF  CONVERTING  IRON  INTO  STEEL 

IN  converting  the  blast-furnace  iron  into  steel  the  Bessemer  process 
has  formerly  been  the  one  most  used,  but  the  improvements  in  the  open- 
hearth  method  have  been  such  that  it  is  replacing  the  Bessemer,  in  many 
places,  for  the  cheap  production  of  steel,  and  the  product  which  it  turns 
out  is  much  better. 

In  the  Bessemer  process  a  converter  similar  to  that  shown  in  Figs. 
9  and  10  is  shown,  it  being  pear-shaped  and  open  at  the  small  end.  It 
is  hung  on  trunnions  so  the  metal  can  be  easily  poured  in  and  out.  Into 
this  is  poured  the  melted  pig  iron,  which  is  usually  taken  direct  from  the 
furnace,  although  it  is  sometimes  remelted,  and  through  this  is  blown 
cold  air  in  fine  sprays  in  the  proportions  of  about  25,000  cubic  feet  of 
cold  air  per  minute  to  every  10  tons  of  molten  metal,  which  is  the  usual 
charge  for  a  converter. 

Curious  as  this  may  seem  to  the  uninitiated,  the  cold  air  raises  the 
temperature  of  the  molten  metal  to  such  a  high  degree  that  it  is  often 
necessary  to  inject  steam  or  add  scrap  to  cool  off  the  metal.  This  rise 
in  temperature  is  due  principally  to  the  combustion  of  the  silicon,  manga- 
nese and  carbon  of  the  iron  when  they  come  in  contact  with  the  oxygen  of 
the  air.  The  silicon  and  manganese  are  oxidized  and  pass  into  the  slag 
chiefly  during  the  first  four  minutes  of  the  blow,  after  which  the  carbon 
begins  to  oxidize  to  carbon  monoxide  (CO),  which  boils  up  through  the 
metal  and  is  forced  out  of  the  mouth  of  the  converter  in  a  long  bright  flame 
that  gradually  diminishes,  until  at  the  end  of  six  minutes  more  the  carbon 
has  been  reduced  to  about  0.04%  and  the  flame  dies  away. 

Except  for  the  impurities  which  poison  the  metal,  namely  phosphorus, 
sulphur,  oxygen  and  possibly  nitrogen,  it  has  become  for  all  practical 
purposes  a  pure  metal  that  is*very  brittle.  This  makes  it  necessary  to 
add  certain  ingredients  that  will  toughen,  strengthen,  and  harden  it  so 
as  to  make  it  useful  and  workable. 

Carbon  is  added  in  different  percentages  while  it  is  in  the  molten  state 
to  give  it  the  proper  degree  of  hardness  and  strength. 

Manganese  is  added  for  the  purpose  of  removing  the  oxygen  which 
the  metal  has  absorbed  during  the  process  of  conversion,  and  which 
renders  it  unfit  for  use.  It  also  combines  with  the  sulphur  and  partly 
neutralizes  the  bad  effects  of  this  element. 

13 


14 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


Silicon  is  also  added  for  the  purpose  of  freeing  the  metal  from  blow- 
holes, which  it  does  partly  by  removing  chemically  the  gases  and  partly 


FIG.  9.  —  Bessemer  converter  purifying 
the  metal. 

through  increasing  their  solubility  in  the  molten  steel.     Of  these  last 
two  elements  but  one-half  to  two-thirds  of  the  percentages  added  will  be 


Shoulder 


Belly 


FIG.  10.  —  Bessemer  converter  tilted  to  pour 
finished  metal  into  ladle. 

found  in  the  finished  product,  owing  to  their  being  partially  oxidized  and 
passing  out  into  the  slag. 


BESSEMER   PROCESS   OF   CONVERTING   IRON   AND   STEEL        15 

These  ingredients  are  added  to  the  charge  in  the  converter  by  first 
melting  iron  containing  them  in  the  proper  amounts  in  a  small  cupola  in 
the  converter  house,  called  the  spiegel  cupola.  Pig  iron  high  in  manganese 
and  carbon,  called  spiegeleisen,  is  mixed  with  other  iron  high  in  silicon 
until  the  right  percentages  of  all  three  are  obtained  to  give  the  10  tons  of 
metal  in  the  converter  its  desired  composition.  The  addition  of  this 


Bessemer  converters  at  Lackawana  Steel  Co. 

mixture  is  called  recarburizing.  After  this  the  converter  is  tilted,  as 
shown  in  Fig.  10,  and  the  steel  poured  into  ladles.  These  are  bottom- 
pour  ladles,  as  shown  in  Fig.  12.  In  these,  as  the  name  signifies,  the  metal 
is  poured  from  the  ladle  through  a  hole  in  the  bottom.  This  saves  turn- 
ing the  ladle  over  and  also  draws  the  molten  metal  away  from  the  slag. 
From  the  ladles  the  metal  is  run  into  cast-iron  ingot  molds  placed  on  cars, 
which  are  moved  beneath  the  pouring  ladle.  After  the  metal  has  solidi- 


16 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


fied  in  the  molds  the  ingots  are  removed  and  placed  in  soaking  pits, 
where  they  become  of  an  equal  temperature  throughout,  and  are  then 
ready  for  rolling.  The  ingot  molds  usually  are  kept  going  through  the 


FIG.  11.  — Tilting  ladles. 

converter  house  in  a  steady  stream;  coming  in  one  side  empty,  getting 
filled  and  going  out  the  other  side. 

Pig  iron  with  about  1%  of  silicon  is  preferred  for  the  Bessemer  pro- 
cess, as  the  lower  this  is  kept  the  shorter  will  be  the  blow,  and  as  it  is  the 
chief  slag  producer  it  will  reduce  the  iron  loss  by  limiting  the  amount  of 
slag  made.  If  too  low,  however,  the  blow  will  be  cold  and  it  is  only  by 
working  rapidly  and  allowing  no  unnecessary  waits  between  blows,  thus 


BESSEMER   PROCESS   OF   CONVERTING   IRON   INTO   STEEL        17 

keeping  the  converter  and  ladles  very  hot,  that  as  low  as  1%  of  silicon  in 
the  pig  iron  can  be  used  successfully. 

In  the  acid  Bessemer  process  it  is  impossible  to  reduce  the  phosphorus. 
All  of  the  phosphorus  that  goes  into  the  blast  furnace  in  the  ore  and  coke 
will  come  out  in  the  pig  iron,  and  after  this  pig  iron  has  been  refined  in  the 
converter  it  will  be  found  in  the  steel.  Hence  it  is  necessary  to  start  with 
ores  and  coke  that  are  low  in  phosphorus  if  a  good  steel  is  to  be  produced. 

In  Europe,  however,  the  basic  Bessemer  converter  is  used  to  a  cer- 
tain extent.  This  is  the  same  as  the  acid,  except  that  the  lining  of  the 


FIG.  12.  —  Bottom-pour  ladles. 

furnace  is  of  some  basic  material  such  as  calcined  dolomite.  A  basic 
slag  is  also  carried,  the  chemical  action  of  which  removes  the  phosphorus, 
but  pig  iron  low  in  silicon  must  be  used. 

The  Bessemer  process  being  the  cheapest  way  of  converting  iron 
into  steel,  much  of  the  cheaper  and  ordinary  grades  of  steel  are  made  by  it, 
such  as  steel  rails,  wire,  merchant  bar,  etc. 

Where  several  Bessemer  converters  are  in  operation  it  takes  quite 
a  number  of  blast  furnaces  to  supply  them,  as  it  takes  two  furnaces  to 
furnish  iron  enough  for  one  converter.  As  the  product  of  each  furnace 
is  liable  to  vary  in  chemical  composition,  it  is  necessary  to  have  some 


18 


COMPOSITION   AND   HEAT-TREATMENT  OF  STEEL 


means  of  mixing  the  product  of  the  different  furnaces,  before  they  are 
poured  into  the  converter,  if  a  uniform  grade  of  steel  is  to  be  taken  out 
of  the  converter/  For  that  reason  a  large  reservoir,  shaped  something 
like  the  housewife's  chopping  bowl,  but  with  a  large  spout  on  it,  and 
capable  of  holding  from  200  to  500  tons,  is  used.  Into  this  is  poured  the 
metal  from  the  various  furnaces  and  from  it  are  taken  the  charges  for 
the  converters. 

This  keeps  the  molten  metal  continually  coming  in  and  going  out, 
and  it  does  not  get  a  chance  to  chill,  as  there  is  such  a  large  mass.     But 


FIG.  13.  —  Stripping  the  mold  from  ingots. 

should  this  happen  it  is  supplied  with  gas  burners  that  would  bring  the 
heat  up  to  the  proper  temperature  again.  The  metallurgist  is  thus  able 
to  control  the  composition  to  a  large  degree,  as  he  can  order  the  different 
furnaces  to  dump  in  the  mixer  the  amount  he  desires.  In  conjunction 
with  this  he  also  has  cupolas  in  which  to  melt  any  composition  needed 
to  bring  the  mixer  bath  up  to  the  desired  standard. 

When  the  ingots  are  poured  and  solidified  the  molds  are  at  a  red  heat, 
and  it  has  been  a  problem  to  find  a  metal  for  the  molds  that  would 
stand  the  heat.  Cast  iron  is  used,  but  the  molds  can  only  be  used  about 
100  times.  Titanium  treated  iron  is  said  to  last  much  better  as  it  does 
not  heat  up  as  quickly.  Quite  recently  one  of  the  large  mills  added  about 


BESSEMER   PROCESS   OF   CONVERTING   IRON   INTO    STEEL        19 

1%  titanium  to  their  ingot  mold  iron,  and  when  the  ingots  were  poured  it 
was  found  that  the  ordinary  iron  molds  were  red  hot,  while  the  titanium 
iron  molds  were  dark  colored. 

As  no  fuel  is  used  in  the  Bessemer  process  of  converting  blast-furnace 
iron  into  steel,  it  is  the  cheapest  method  of  making  steel  as  far  as  manufac- 
turing cost  is  concerned,  but  it  requires  a  more  expensive  pig  iron  as  raw 
material  and  it  also  makes  the  poorest  grade  of  steel,  as  the  phosphorus 
and  sulphur  are  apt  to  be  higher  than  in  steels  made  by  the  other  processes, 
and  the  occluded  gases  are  not  removed  to  the  same  extent. 

For  the  purpose  of  getting  these  occluded  gases  out  of  the  metal  a 
new  material  has  been  brought  into  use,  in  the  shape  of  ferro-titanium, 


FIG.  14.  —  Soaking  pit  for  ingots. 

that  greatly  strengthens  the  metal  and  increases  its  wearing  quality, 
when  used  for  such  purposes  as  steel  rails.  This  ferro-titanium  is  an 
alloy  of  about  15%  titanium  with  iron  and  usually  some  carbon.  It  is 
never  necessary  to  add  more  than  1%  of  titanium  to  the  steel,  while  in 
most  cases  very  much  less  will  give  the  desired  results. 

It  is  shoveled  into  the  ladle  while  it  is  being  filled  from  the  converter 
and  the  ladle  allowed  to  stand  for  at  least  6  minutes,  so  the  titanium  will 
have  time  to  unite  with  the  nitrogen  and  other  gases,  for  which  it  has  a 
great  affinity,  and  carry  these  off  into  the  slag.  It  is  difficult  to  get 
steel  makers  to  allow  a  ladle  of  molten  metal  to  stand  idle  that  length  of 
time,  but  the  titanium  prevents  its  chilling  and  in  fact  may  leave  the  mol- 
ten metal  slightly  hotter  at  the  end  of  the  6  minutes  than  when  it  left 


20  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

the  converter.     In  one  case  the  metal  was  held  in  the  ladle  for  20  minutes 
and  was  still  sharp  enough  to  teem  successfully. 

Sulphur  must  be  kept  low  in  steel  for  rails  and  other  products  which 
are  rolled,  since,  if  high,  it  makes  the  metal  " hot-short"  so  that  it  cracks 
in  rolling.  Phosphorus,  on  the  other  hand,  if  too  high  makes  steel  "  cold- 
short," and  some  railroad  accidents,  caused  by  broken  rails,  could  be 
traced  to  too  high  a  percentage  of  phosphorus.  High-phoshporus  rails, 


FIG.  15.  —  Carrying  ingot  from  soaking  pit  to  slabbing  mill. 

however,  have  good  wearing  qualities,  and  when  titanium  is  properly  added 
to  the  molten  metal  it  seems  to  remove  to  some  extent  the  hot  and  cold 
brittleness  that  a  comparatively  high  percentage  of  sulphur  and  phos- 
phorus give  to  the  metal. 

Many  of  the  fractures  in  steel  rails  have  been  due  to  miniature  gas 
bubbles  in  the  steel,  that  have,  when  rolled,  produced  long  microscopic 
cracks,  and  started  the  fracture;  others  have  been  caused  by  manganese 
sulphide  which  rolled  out  into  long  threads. 

However,  by  the  use  of  titanium  these  faults  can  be  largely  overcome 


BESSEMER   PROCESS   OF    CONVERTING    IRON    INTO    STEEL        21 

and  Bessemer  rails  can  be  made  as  good,  if  not  better,  than  open-hearth 
rails,  and  the  additional  cost  is  only  about  $2  per  ton.  A  part  of  this  added 
cost  comes  from  the  extra  time  consumed  in  allowing  the  ladle  to  stand. 

After  solidifying  the  ingot  the  mold  cars  are  run  under  the  stripper, 
which  is  located  in  a  tower,  as  shown  in  Fig.  13,  and  from  there  a  long 
finger  comes  down  on  top  of  the  ingot  to  hold  it,  while  two  iron  loops  come 
down  over  lugs  on  either  side  of  the  mold  and  lift  it  off  the  ingot.  The 
ingot  is  then  gripped  by  a  huge  pair  of  tongs  on  a  traveling  crane  and 
these. pick  it  up  and  carry  it  to  the  coaking  pit  shown  in  Fig.  14.  After 
remaining  in  here  long  enough  to  reach  a  proper  rolling  temperature 


FIG.  16.  —  Slabbing  mill. 

throughout,  it  is  placed  on  the  " buggy,"  which  is  an  iron  car  operated 
by  electricity,  and  carried  by  this  to  the  slabbing  mill  where  it  is  automat- 
ically dumped  onto  the  rolls  and  the  buggy  returned  for  another  ingot. 

In  some  cases  an  overhead  traveling  tongs,  similar  to  that  shown  in 
Fig.  15,  is  used  to  convey  the  ingots  from  the  soaking  pit  to  the  slabbing 
mill.  A  typical  modern  slabbing  mill  is  shown  in  Fig.  16. 

It  was  formerly  the  custom  to  roll  them  into  "blooms"  or  large  billets 
about  10  inches  square,  and  reheat  again  before  rolling  them  into  mar- 
ketable shapes,  but  in  the  more  modern  mills  the  ingots  now  are  taken 
directly  to  the  slabbing  mill,  which  in  some  cases  reduces  their  size  1 
inch  at  a  pass,  and  there  rolled  into  slabs,  which  are  transferred  to  other 
rolls  and  rolled  into  the  desired  shape  before  they  get  cold. 


CHAPTER    III 
OPEN-HEARTH  PROCESS  FOR  MAKING  STEEL 

THE  open-hearth  furnace  for  converting  pig  iron  into  steel  is  made 
and  used  in  both  the  stationary  and  tilting  styles,  as  shown  in  Figs.  17 
and  18.  As  the  name  implies,  it  has  an  open  hearth  on  which  the  metal 
is  placed  and  where  it  is  exposed  to  a  flame  which  reduces  it  to  a  molten 
state;  or,  in  other  words,  it  is  openly  exposed  to  the  action  of  burning 
gases. 

This  furnace  must  be  a  regenerative  one  to  get  the  high  temperature 
that  is  needed  to  melt  and  refine  the  metal.  By  this  is  meant  one  in  which 
the  heat  carried  away  by  the  chimney  flue  is  used  to  warm  the  incoming 
air  and  gas  before  they  enter  the  furnace.  This  name  has  been  commonly 
applied  to  the  furnace  as  shown  by  the  sectional  view  in  Fig.  19,  by 
which  both  the  air  and  gas  are  heated  before  entering  the  furnace  by 
sending  them  through  passages  filled  with  bricks  which  are  stacked  up 
so  as  to  leave  openings  between  them.  Two  sets  of  passages  are  provided 
so  that  one  can  be  used  to  absorb  the  heat  in  the  exhaust  gases  while 
the  other  is  warming  the  incoming  air  and  gas.  These  passages  are 
supplied  with  reversing  valves  so  that  they  can  be  used  alternately  and 
thus  heat  the  gas  and  air  to  a  yellow  heat  before  they  unite.  This 
method  gives  a  very  intense  heat. 

From  30  to  75  tons  of  metal  are  purified  in  one  of  these  furnaces  in 
from  6  to  10  hours.  It  is  then  "recarburized,"  or  in  other  words  the 
proper  percentage  of  carbon  is  added,  and  the  metal  poured  into  ingot 
molds  from  which  it  is  taken  and  rolled  or  forged  into  the  sizes  and  shapes 
desired. 

As  two  of  the  main  considerations  in  the  modern  steel  mill  are  output 
and  economy,  the  size  of  furnaces  has  been  increasing  and  Talbot  pro- 
cess open-hearth  furnaces  have  been  built  of  250  tons  capacity,  while 
larger  ones  are  to  follow.  Where  blast  furnaces  and  steel  mills  are  located 
together  the  pig  iron  is  taken  in  the  molten  state  to  the  open-hearth 
furnaces,  and  converted  into  steel  as  fast  as  the  blast  furnaces  turn 
it  out.  This  practice  has  been  an  important  factor  in  obtaining  large 
outputs. 

22 


OPEN-HEARTH   PROCESS   FOR   MAKING  STEEL 


23 


IIIIH2' 


24 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


OPEN-HEARTH   PROCESS   FOR   MAKING   STEEL 


25 


In  the  Talbot  process  the  stationary  furnace  of  the  original  Siemens- 
Marten  process  is  changed  to  a  tilting  form  so  that  the  slag  which  forms, 
and  which  limits  the  rate  of  charging,  can  be  more  easily  handled.  The 
charge  is  worked  down  to  the  desired  percentage  of  carbon  by  means  of 
additions  of  ore  and  limestone  in  the  usual  manner.  The  slag  is  then 
removed  and  about  one-fourth  of  the  steel  poured  off  and  recarburized  in 
the  ladle  as  usual.  To  the  metal  remaining  in  the  furnace  ore  and  lime- 
stone are  now  added  and  through  the  slag  thus  formed,  is  poured  a  fresh 
charge  of  molten  pig  iron.  The  removal  of  the  carbon,  silicon,  etc.,  under 
these  conditions  is  rapid,  but  the  reactions  are  not  violent,  owing  to  the 


FIG.  19.  —  Section  through  regenerative  open-hearth  furnace. 


dilution  by  the  steel  remaining  in  the  furnace.     The  process  is,  continuous 
and  the  furnace  is  completely  emptied  only  once  a  week. 

There  are  also  in  use  tilting  open-hearth  furnaces  with  a  double  hearth, 
as  shown  in  Fig.  20,  with  a  stationary  top,  and  in  Fig.  21  with  a  moving 
top.  The  tilting  serves  here  not  to  discharge  the  furnace,  but  to  carry  on 
different  operations  simultaneously  in  the  one  furnace.  The  amount  of 
tilt  given  the  hearths  governs  the  amount  of  metal  or  slag  to  be  run  from 
one  hearth  to  the  other,  this  amount  depending  upon  the  angle  of  tilt, 
gradient  of  hearth,  length  of  hearth,  and  depth  of  bath. 


26 


COMPOSITION   AND  HEAT-TREATMENT  OF  STEEL 


OPEN-HEARTH  PROCESS  FOR   MAKING  STEEL 


27 


The  method  of  operation  in  the  combined  pig  iron  and  ore  process, 
which  first  suggested  the  furnace,  is  as  follows:  A  charge  is  left  only  suffi- 
ciently long  in  hearth  A  to  reduce  the  iron  from  the  slag,  this  being  already 
decarbonized.  In  order  to  free  the  charge  from  the  iron-bearing  slag  and 
to  pave  the  way  for  the  final  refining,  the  furnace  is  tilted  so  the  slag 
flows  from  hearth  A  to  hearth  B.  After  the  slag  has  been  poured  into 
B,  molten  pig  is  charged,  the  contact  of  the  pig  and  slag  sets  up  an  ener- 
getic refining  action  and  the  iron  is  taken  from  the  slag.  Meanwhile 
the  charge  on  hearth  A  is  finished  and  tapped.  The  hearth  is  repaired 
as  usual  and  the  tap  hole  left  open. 

As  the  operation  is  a  continuous  one,  the  slags  which  have  not  been 
discharged  must  be  poured  when  sufficiently  low  in  iron.  By  a  slight 
tilting  of  the  furnace,  the  slag  runs  from  B  to  A  and  out  through  the 


FIG.  21.  —  Double-hearth  furnace  with  moving  top. 


open  tap  hole.  Or  it  may  be  discharged  over  the  side  walls  of  hearth  B 
and  the  hearth  A  used  at  the  same  time  for  charging  fresh  material.  In 
hearth  B  the  heat  generated  by  the  decarbonization  of  the  iron  is  made 
use  of  by  the  scattering  of  iron  ore  over  the  charge  as  long  as  the  tem- 
perature holds.  As  all  of  the  iron  cannot  be  reduced  from  the  ore,  a  cer- 
tain amount  of  ore  is  slagged.  The  desired  slag,  heavy  with  iron,  is 
thus  obtained.  It  will  be  later  poured  off  into  hearth  A  where  the  opera- 
tion is  steadily  going  on,  molten  pig  added,  and  the  process  continued 
as  before. 

Steel  is  made  in  two  ways  in  the  open-hearth  furnace:  one  is  called 
the  acid  open-hearth  process  and  the  other  the  basic  open-hearth  process. 
About  30%  of  the  pig  iron  made  in  this  country  is  converted  into  steel 
by  the  basic  process,  and  2  or  3%  by  the  acid.  For  the  making  of  open- 


28  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

hearth  steel  castings  the  acid  process  was  used  almost  exclusively,  but  it 
is  now  giving  way  to  the  basic  process  owing  to  the  fact  that  ores  low  in 
phosphorus  and  sulphur  are  becoming  higher  priced  each  year,  and  these 
elements  cannot  be  reduced  in  the  acid  furnace. 

The  number  of  charges  these  furnaces  will  make  into  steel  before 
having  to  be  rebuilt  is  about  300  for  the  basic  furnace,  which  would  cover 
a  period  of  from  15  to  20  weeks,  and  about  1000  heats  from  the  acid  open- 
hearth  furnace,  before  doing  any  more  to  them  than  the  usual  patching 
at  the  end  of  the  week's  run. 

Pig  iron  and  steel  scrap  are  the  chief  raw  materials  with  the  addition 
of  enough  iron  ore  to  quicken  the  operation.  In  America,  on  an  average, 


FIG.  22.  —  Machine  for  charging  open-hearth  furnaces. 

about  one-half  the  charge  is  steel  scrap  but  sometimes  as  high  as  90% 
is  used.  This  latter,  however,  is  but  little  more  than  a  remelting  opera- 
tion. In  most  American  mills  the  steel  scrap  is  first  placed  on  the  hearth 
and  this  then  covered  with  pig  iron,  as  the  oxidation  of  iron  is  decreased 
while  melting  by  the  impurities  in  the  pig  iron.  In  some  American  and 
most  of  the  English  mills  the  pig  iron  is  put  on  the  hearth  first  and  this 
covered  with  the  steel  scrap,  with  the  understanding  that  the  hearth  is 
corroded  less  with  oxide  of  iron,  but  unless  the  scrap  is  small  not  much 
corrosion  will  take  place. 

In  charging  the  acid  furnace  it  is  best  to  put  the  scrap  on  the  hearth 
and  the  pig  on  top  of  it,  while  in  the  basic  furnace  we  may  put  in  a  part 
of  the  scrap  first,  the  limestone  on  top  of  that,  then  the  pig,  and  cover 


OPEN-HEARTH    PROCESS   FOR    MAKING   STEEL  29 

the  whole  with  the  balance  of  the  scrap,  or  we  may  charge  the  limestone 
on  the  hearth,  the  pig  next,  and  cover  the  scrap  over  the  top. 
The  charging  machine  used  is  shown  in  Fig.  22. 


ACID    OPEN-HEARTH 

In  this  process  the  furnace  is  lined  with  silicious  materials  (sand). 
This  lining  influences  the  subsequent  operations  as  the  character  of  the 
bottom  determines  the  character  of  the  slag  that  can  be  carried,  which, 
in  turn,  determines  the  chemistry  of  the  process.  The  metal  is  heated 
by  radiation  from  the  high  temperature  flame.  The  impurities  are  par- 
tially oxidized  by  an  excess  of  oxygen  over  that  which  is  necessary  to  burn 
the  gas  in  the  furnace.  This  oxidizes  the  slag  wrhich,  in  turn,  oxidizes 
the  impurities  in  the  metal. 

The  slag  is  about  one-half  silica  (Si02)  and  the  other  half  is  com- 
posed of  oxides  of  iron  and  manganese.  Nothing  is  added  to  form  a 
slag  as  the  combustion  of  the  silicon  and  manganese  with  what  iron  is 
oxidized  and  some  sand  from  the  lining  in  the  bottom  gives  the  necessary 
supply. 

When  the  metal  is  melted  iron  ore  is  added,  and  the  oxygen  in  the  ore 
oxidizes  the  excess  of  carbon  until  the  proper  percentage  is  acquired. 
Recarburization  is  carried  out  in  the  furnace  by  the  addition  of  a  proper 
amount  of  ferro-manganese,  together  with  any  other  materials  that  may 
be  necessary. 

In  the  acid  process  the  percentage  of  phosphorus  and  sulphur  depends 
upon  what  the  stock  contains  that  is  plit  in  the  furnace,  as  neither  of 
these  are  removed ;  but  the  amount  of  carbon  in  the  steel,  and  therefore  its 
tensile  strength,  depends  entirely  on  the  conduct  of  the  operation.  This 
latter  is  usually  reduced  to  the  right  percentage  and  the  charge  then  tapped 
out,  but  it  may  be  reduced  below  the  amount  required  and  enough  then 
added  to  make  up  the  proper  percentage. 

The  gradual  increase  in  the  temperature  of  the  furnace  caused  by  the 
regeneration  of  the  secondary  air  first  causes  the  oxidation  of  the  silicon, 
which  occurs  mostly  on  the  surface  of  the  metal,  by  the  oxidizing  action 
of  the  flame.  This  causes  the  slag  mentioned  above  to  form  and  cover  the 
surface  of  the  bath,  thus  protecting  the  metal  from  any  further  contact 
with  the  flame  from  which  it  might  absorb  some  of  the  gases,  and  be  in- 
jured. After  the  silicon  oxidizes  out,  the  carbon  begins  to  work  out  as  a  gas 
that  causes  bubbling  or  boiling  throughout  the  bath.  By  the  addition  of 
iron  ore  this  action  can  be  augmented  as  occasion  requires.  When  the 
carbon  has  been  reduced  to  the  percentage  desired,  the  boil  is  stopped 
by  deoxidizing  agents,  such  as  ferro-silicon  or  ferro-manganese, 


30  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

The  points  in  favor  of  the  acid  open-hearth  process  of  making  steel 
are  that  the  operations  are  shorter,  owing  to  the  fact  that  the  phosphorus 
cannot  be  reduced  and  no  fluxes  are  added,  except  possibly  a  little  silica 
at  the  beginning  to  prevent  the  lining  from  being  cut  by  the  iron  oxide. 
The  bath  being  more  free  from  oxygen  at  the  end  of  the  heat,  less  trouble 
is  encountered  from  blow-holes. 

Most  engineers  and  machinery  designers  agree  that  acid  open-hearth 
steel  of  a  given  composition  is  more  reliable,  less  liable  to  break  and  more 
uniform  than  either  Bessemer  or  basic  open-hearth  steel,  and  this  is  doubt- 
less due  to  its  being  more  free  from  the  occluded  gases,  although  these 
are  not  removed  as  much  in  the  open-hearth  as  in  the  crucible  or  electric 
furnace  processes. 

The  principal  and  possibly  the  only  reason  this  process  is  not  used 
more,  and  especially  in  this  country,  is  that  ores  low  enough  in  phosphorus 
are  scarce  and  consequently  expensive.  As  the  prices  of  these  ores  are 
gradually  increasing,  and  have  been  for  some  time,  the  acid  open-hearth 
process  is  steadily  becoming  of  relatively  less  importance. 

It  is  usually  easy  to  tell  the  difference  between  basic  and  acid  steel, 
but  it  is  difficult  to  tell  the  difference  between  basic  Bessemer  and  basic 
open-hearth  steel  or  between  acid  Bessemer  and  acid  open-hearth  steel. 
Therefore,  one  has  to  depend  on  the  honesty  of  the  steelmakers,  unless 
they  wish  to  go  into  exhaustive  tests  of  each  piece  of  steel  received. 


BASIC    OPEN-HEARTH 

A  regenerative  open-hearth  furnace,  similar  to  that  shown  in  Fig.  19 
for  the  acid  process,  is  used  for  the  basic,  but  the  lining  is  of  a  different 
material.  It  is  composed  of  some  basic  material  that  is  usually  either 
magnesite  or  burned  dolomite. 

The  lining  or  bottom  of  the  furnace  takes  little  part  in  the  operation, 
but  determines  the  character  of  the  slag  which  can  be  carried.  When 
the  bottom  is  silica  (sand)  the  slag  must  be  silicious  and  when  the  bottom 
is  basic  the  slag  must  be  basic.  The  charge  put  in  the  basic  open-hearth 
furnace  is  composed  of  pig  iron  mixed  with  steel  scrap  or  similar  iron  pro- 
ducts, the  same  as  in  the  acid  furnace.  But  in  addition  to  this,  lime  or 
limestone  is  added,  in  order  to  make  a  very  basic  slag. 

This  slag  will  dissolve  all  the  phosphorus  that  is  oxidized,  a  thing  that 
an  acid  slag  will  not  do.  In  the  acid  open-hearth  or  Bessemer  process 
the  silicious  slag  rejects  the  phosphorus  which  is  immediately  deoxidized 
and  returns  to  the  iron.  Sulphur  is  also  removed  to  a  limited  extent, 
and  pig  iron  with  these  impurities  can  be  used  in  the  basic  open-hearth 
furnace.  When  the  sulphur  is  high  the  slag  must  be  charged  with  all  the 


OPEN-HEARTH    PROCESS   FOR    MAKING  STEEL  31 

lime  it  will  stand  without  becoming  infusible  and  pasty.  The  slag  can 
contain  as  high  as  55%  of  lime  (CaO)  for  this  purpose.  If  the  manganese 
is  above  1%  it  makes  the  slag  more  fluid  and  aids  in  the  removal  of 
sulphur. 

If  the  slag  is  basic  enough  not  to  attack  the  bottom  it  will  hold  the 
phosphorus,  providing  the  stock  does  not  contain  over  one  half  of  1%. 
With  a  higher  percentage  special  attention  must  be  given  to  the 
phosphorus  to  prevent  its  passing  back  into  the  steel  when  a  high 
temperature  is  combined  with  violent  agitation,  as  is  used  when  the  heat 
is  tapped. 

Although  the  phosphorus  and  sulphur  are  lower  in  the  basic  steel, 
the  acid  steel  is  considered  better,  owing  to  the  increased  liability  of 
blow-holes  and  gas  bubbles  in  steel  converted  by  the  basic  process. 
Then  again  the  process  of  recarburizing  sometimes  produces  irregu- 
larities. The  metal  is  also  more  highly  charged  with  oxygen.  All  of 
these  make  a  poorer  quality  of  steel  than  is  produced  by  the  acid  open- 
hearth  process,  but  a  far  better  one  than  is  being  made  in  the  Bessemer 
converter. 

In  the  purification  of  the  metal  the  silicon  and  manganese  are  first 
almost  entirely  oxidized  in  the  4  hours  or  so  that  it  takes  the  metal  to 
melt,  while  the  phosphorus  and  carbon  are  reduced  to  some  extent.  After 
this  phosphorus  is  eliminated,  and  lastly  the  carbon  is  removed.  It  is 
necessary  that  the  phosphorus  be  eliminated  before  the  carbon  as  the  lat- 
ter protects  the  iron  the  most,  thus  reducing  the  loss  due  to  melting.  The 
melter  controls  this-  by  adding  pig  iron  to  increase  the  carbon  contents 
if  this  is  being  removed  too  fast;  or  he  can  add  ore  to  produce  the  neces- 
sary reaction  to  hasten  the  oxidization  of  the  carbon. 

After  being  purified  the  metal  must  be  recarburized  to  get  back  into 
it  the  percentages  of  the  elements  that  are  desired.  This  must  not  be 
done  when  a  basic  slag  is  present,  or  the  manganese,  carbon,  and  silicon 
in  the  recarburizer  are  liable  to  cause  the  phosphorus  in  the  slag  to  pass 
back  into  the  molten  metal.  Therefore  the  recarburizer  is  added  to 
the  molten  metal  as  it  is  flowing  from  the  furnace  into  the  ladle,  and  the 
slag  is  allowed  to  float  off  from  the  top.  As  the  spiegeleisen  cupola 
cannot  be  used  with  the  open-hearth  furnace,  the  recarburizer  usually 
consists  of  a  combination  of  small  lumps  of  coal,  charcoal,  or  coke  in 
paper  bags  and  ferro-manganese. 

When  soft  steel  is  being  made  the  carbon  in  the  bath  is  usually  reduced 
to  from  0.10%  to  0.15%,  and  enough  of  the  carburizer  is  then  added  to 
bring  this  up  to  the  percentage  desired  in  the  finished  steel.  When  high 
carbon  steels  are  being  made,  another  method  is  sometimes  used,  and 
that  is  to  bring  the  carbon  in  the  bath  just  below  the  percentage  desired, 
and  then  recarburize  up  to  it.  Thus  when  a  1%  carbon  steel  is  to  be 


32 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


made,  the  carbon  in  the  bath  is  reduced  to  from  0.90  to  0.95%,  and  enough 
added  with  the  carburizer  to  raise  it  to  1%.  Many  steel  makers,  however, 
reduce  the  carbon  in  the  bath  to  the  same  point,  namely,  0.10  to  0.15%, 
when  making  both  high  and  low  carbon  steels,  and  then  get  the  correct 
percentage  by  the  addition  of  the  proper  amount  of  carburizer. 

Among  other  open-hearth  processes  might  be  mentioned  the  Monell 
process,  in  which  limestone  and  a  comparatively  large  amount  of  iron 
ore  are  heated  on  a  basic  hearth  until  they  begin  to  melt,  and  then  the 
molten  pig  iron  is  poured  onto  it;  the  duplex  process  in  which  an  acid 
Bessemer  converter  is  used  to  oxidize  the  silicon  manganese  and  part  of 
the  carbon,  and  the  metal  then  poured  into  a  basic  open-hearth  furnace 
to  reduce  the  phosphorus  and  the  balance  of  the  carbon;  the^ Campbell 


FIG.  23.  —  One  of  the  largest  ingots  cast. 

No.  1  process,  in  which  a  tilting  furnace  is  used  with  a  charge  of  molten  pig 
iron  and  ore,  the  furnace  being  tipped  backward  to  prevent  the  bath  from 
frothing  out  of  the  door,  and  the  operation  continued  for  two  or  three 
hours,  and  the  Campbell  No.  2  process,  which  aims  to  combine  the  basic 
and  acid  open-hearth  processes  by  working  pig  iron  or  pig  iron  and  scrap 
in  the  basic  furnace  at  a  low  temperature  until  most  of  the  phosphorus 
and  silicon  and  part  of  the  carbon  and  sulphur  are  oxidized  out,  then 
transferring  the  bath  to  an  acid  furnace  and  working  it  at  a  high  tempera- 
ture to  remove  the  rest  of  the  carbon.  The  object  is  to  get  a  low- 
phosphorus,  low-sulphur  steel. 

One  of  the  largest  ingots  that  has  been  cast  from  the  open-hearth 
furnaces  is  shown  by  Fig.  23. 

One  of  the  greatest  troubles  of  the  steel  maker  is  the  pipe  that  forms 


OPEN-HEARTH  PROCESS  FOR  MAKING  STEEL  33 

in  the  top  of  each  ingot  and  forces  him  to  crop  off  and  remelt  a  large  part 
of  it.  Numerous  ways  have  been  tried  to  overcome  this  and  the  most 
successful  of  these  is  the  fluid  compressor  of  which  Fig.  24  is  an  example. 


FIG.  24.  —  Machine  for  compressing  ingots  when  fluid. 

This  consists  of  a  large  ingot  mold,  built  in  sections,  into  which  the  molten 
metal  is  poured.  While  the  metal  is  solidifying  a  ram  is  pressed  down 
into  the  mold  by  means  of  four  screws.  This  compresses  the  metal  as 
fast  as  it  shrinks,  and  thus  removes,  or  at  least  partly  removes,  the  pipe 
by  not  allowing  it  to  form. 


CHAPTER  IV 

CRUCIBLE  PROCESS  OF  STEEL  MAKING 

IN  the  crucible  process  a  regenerative  furnace  is  sometimes  used  sim- 
ilar to  the  one  shown  in  Figs.  25  and  26.  In  this  the  heat  does  not  attack 
the  top  of  the  metal  as  in  the  open-hearth,  but  heats  crucibles  which  are 
covered  and  the  cover  sealed  on  with  fire  clay,  so  that  the  gases  from  the 
fuel  will  not  attack  the  metal.  In  some  places,  however,  coke  furnaces 
or  melting  holes  containing  crucibles  are  used. 

In  Europe  these  crucibles  are  made  of  fire-clay  by  the  steel  makers, 
as  they  are  comparatively  cheap  and  no  carbon  is  absorbed  by  the  metal, 
as  is  the  case  with  the  graphite  crucibles  used  in  this  country,  and  conse- 
quently this  element  can  be  more  easily  controlled  in  the  finished  product. 
They  are  usually  made  to  hold  50  pounds  of  metal,  as  that  is  about  the 
limit  for  the  strength  of  the  clay  crucible.  The  molten  slag  on  top  of  the 
metal  cuts  deeply  into  the  clay,  and  the  second  charge  has  to  be  cut  down 
to  about  45  pounds  to  get  below  the  slag-line,  while  for  a  third  charge 
38  pounds  is  about  the  limit,  and  after  this  they  are  thrown  away,  as  it 
is  not  economical  to  use  them.  One  or  two  steel  makers  in  Europe  only 
use  the  clay  crucibles  once,  as  they  claim  they  can  get  a  better  steel, 
owing  to  the  larger  air  space  causing  greater  oxidization  and  the  tendency 
of  the  metal  to  absorb  and  occlude  some  of  the  gases. 

The  graphite  crucibles  which  are  used  to  a  large  extent  in  this  country 
are  made  by  concerns  that  make  a  specialty  of  this  business,  and  from  a 
mixture  that  is  about  one-half  graphite  and  one-half  fire-clay.  These 
generally  hold  100  pounds  and  last  for  about  6  heats,  but  as  carbon  is 
given  up  by  the  crucible  and  enters  the  molten  metal,  it  is  more  difficult 
to  control  this  than  when  clay  crucibles  are  used. 

The  crucible  process  is  used  only  for  the  making  of  high-grade  and 
special  alloyed  steels,  such  as  high-speed,  nickel,  or  vanadium  chrome, 
etc.  It  is  about  three  times  as  expensive  as  the  next  cheapest,  namely, 
acid  open-hearth,  but  for  such  work  as  cutting  tools,  armor-piercing  pro- 
jectiles, gears  that  are  subjected  to  heavy  or  vibrational  strains,  high- 
grade  springs  and  many  other  uses  the  crucible  steels  far  excel  anything 
that  is  made  by  the  other  processes.  The  reason  for  this  superiority 
is  largely  due  to  the  fact  that  it  is  made  in  covered  pots,  which  exclude 

34 


CRUCIBLE  PROCESS  OF  STEEL  MAKING 


35 


36 


COMPOSITION  AND   HEAT-TREATMENT  OF   STEEL 


the  furnace  gases  and  air.     It  is  therefore  freer  from  oxygen,  hydrogen, 
and  nitrogen  in  the  form  of  occluded  gases. 

The  material  used  for  conversion  into  steel  by  the  crucible  process  is 
usually  wrought  iron  and  not  pig  iron  as  in  the  Bessemer  and  open-hearth 
processes.  The  wrought  iron,  in  the  form  of  muck  bars,  is  cut  up  into 


A 


FIG    26.  —  Regenerative  gas  furnace  for  crucibles. 

small  pieces  and  placed  in  the  crucible  with  the  desired  amount  of  carbon, 
which   is   generally  in   the  form    of   charcoal,  but  sometimes   is   intro-. 
duced  through  the  medium  of  pig  iron.     Some  ferro-manganese  or  spie- 
geleisen  are  also  added  and  when  alloyed  steels  are  desired  such  alloying 
elements  as  tungsten,  chromium,  nickel,  etc.,  are  added.    Sometimes  a  small 


FIG.  27.  —  The  charged  crucible. 

amount  of  glass  or  other  similar  material  is  used  to  give  a  passive  slag, 
and  various  physics,  such  as  salt,  potassium  ferro-cyanide,  oxide  of  man- 
ganese, etc.,  are  used  by  some.  The  ferro-manganese  adds  the  desired 
amount  of  manganese  to  the  steel  and  it  is  thought  that  the  salt  and 
oxide  of  manganese  make  a  more  fluid  slag,  while  the  ferro-cyanide  might 


CRUCIBLE   PROCESS   OF   STEEL   MAKING 


37 


aid  the  steel  in  absorbing  the  carbon.  In  the  pot  are  also  a  little  air,  some 
slag  and  oxide  of  iron,  this  last  being  the  scale  and  rust  on  the  surface 
of  each  piece  of  metal,  and  silica,  and  alumina  from  the  scorification  of 
the  walls  of  the  crucible.  Sometimes  some  cheaper  steel  scrap  is  mixed 
with  the  wrought  iron,  but  this  always  lowers  the  quality  of  the  finished 
steel.  A  crucible  that  has  been  charged  and  is  ready  for  melting  is  shown 
in  Fig.  27. 


FIG.  28.  —  Pouring  ingots  from  crucibles. 

Some  time  is  required  for  the  reduction  of  the  silicon  from  the  slag  and 
lining  as  well  as  for  the  various  reactions  which  occur.  When  this  reduc- 
tion has  reached  a  point  where  the  steel  contains  from  0.20  to  0.40% 
of  silicon  and  the  metal  lies  quiet  and  "dead,"  that  is,  the  evolution  of 
the  gases  have  stopped  so  it  will  pour  quietly  and  cast  into  solid  ingots, 
the  crucible  is  taken  from  the  furnace  and  the  contents  poured  into  ingot 
molds,  as  shown  in  Fig.  28.  After  these  have  cooled  they  are  usually 


38 


COMPOSITION   AND   HEAT-TREATMENT   OF  STEEL 


reheated  in  a  furnace  and  reduced  to  a  size  suitable  for  rolling  by  hammer- 
ing under  a  steam  hammer,  as  shown  in  Fig.  29.  This  reduces  the  grain 
and  makes  the  metal  more  dense. 

Crucible  steel  usually  contains  less  than  0.40%  manganese,  more  than 
0.20%  silicon,  less  than  0.025%  phosphorus,  and  less  than  0.030%  sul- 


FIG.  29.  —  Hammering  the  ingot. 

phur,  while  the  carbon  content  is  usually  made  high,  owing  to  the  uses 
to  which  crucible  steels  are  put. 

The  main  difficulty  with  this  process  is  in  making  large  ingots  so  these 
ingredients  will  be  combined  in  a  homogeneous  mass.  As  the  personal 
element  is  a  factor  in  the  charging  of  the  crucibles,  and  these  hold  only 
100  pounds  or  less,  the  steel  made  in  each  crucible  is  liable  to  vary  some 


CRUCIBLE  PROCESS  OF  STEEL   MAKING 


39 


in  the  composition  of  its  ingredients.  Thus  when  a  1000  pound  ingot  is 
to  be  cast  it  requires  10  or  more  crucibles  to  fill  it  and  the  metal  does 
not  have  a  chance  to  mix  thoroughly  before  getting  cold,  which  will  result 
in  certain  of  the  ingredients  showing  a  higher  percentage  in  some  part  of 
the  ingot  than  in  others  unless  great  care  is  exercised  in  charging  each 
of  the  10  crucibles. 

A  large  part  of  the  crucible  steel  is  hammered  into  bars,  as  shown  in 
Fig.  30,  and  the  accuracy  and  quickness  with  which  a  hammersman  can 
turn  out  these  bars  is  one  of  the  surprising  features  of  the  steel  business. 


30.  —  Hammering  octagon  bars. 


They  usually  work  by  the  ton,  and  it  is  difficult  for  the  inexperienced  man 
to  tell  the  bars  from  rolled  stock. 

This  process  has  changed  very  little  in  the  last  100  years  or  more, 
and  its  chemistry,  which  consists  principally  of  eliminating  the  slag  in 
the  wrought  iron  and  adding  carbon  silicon  and  manganese  to  the  metal, 
is  very  simple.  The  progress  which  has  been  made  in  crucible  steel 
is  due  almost  entirely  to  the  discovery  of  new  alloying  materials  that  have 
added  strength,  toughness,  wearing  qualities,  cutting  qualities,  etc., 
to  the  metal.  Thus  more  different  kinds  of  good  steels,  and  better 


40  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

steels,  are  being  made  to-day  by  this  process,  which  is  way  above  all  the 
other  processes  for  making  steel  of  quality,  than  at  any  time  previous. 

The  enormous  and  wonderful  change  that  has  been  made  in  the  steel 
business  is  due  to  the  perfecting  of  methods  and  machinery  for  making 
steel  quicker,  cheaper,  and  in  larger  quantities.  However,  when  we  want 
an  extra  fine  grade  of  steel  we  have  to  fall  back  on  the  crucible  process 
which  is  still  carried  out  in  practically  the  same  manner  as  was  the  case 
many  years  ago.  The  progress  that  has  been  made  in  electricity  and  the 
experiments  that  have  been  carried  on  with  the  electric  refining  furnace, 
however,  would  seem  to  indicate  that  in  the  not  very  distant  future  this 
might  do  away  with  the  slow,  laborious,  and  costly  crucible  process;  if 
not  entirely,  at  least  to  a  large  extent. 

WROUGHT   IRON 

The  wrought  iron  used  in  making  crucible  steel  or  for  other  purposes 
is  also  made  by  the  same  process  and  in  much  the  same  manner  that  it 
was  100  or  more  years  ago.  A  reverberatory  furnace  hearth  is  "fettled" 
or  lined  with  oxide  of  iron,  that  is,  either  good  iron  ore,  roasted  puddle 
cinder,  or  roll  scale.  On  this,  pig  iron  is  melted,  and  some  of  the  man- 
ganese and  silicon  being  oxidized  a  slag  with  a  high  content  of  iron  oxide 
is  formed  by  absorbing  this  constituent  from  the  lining.  The  impurities 
are  then  removed  to  a  greater  or  less  extent  through  a  reaction  between 
the  carbon,  manganese,  silicon,  sulphur,  and  phosphorus  in  the  molten 
iron  and  the  oxide  of  iron  in  the  slag.  This  basic  slag  carries  oxygen 
to  the  impurities  and  is  assisted  by  the  excess  of  oxygen  in  the  furnace 
gases. 

As  the  iron  approaches  nearer  to  purity  it  thickens,  as  the  purer  the 
iron  the  higher  will  be  its  melting  temperature,  and  the  heat  in  the  fur- 
nace is  not  sufficient  to  keep  it  molten.  When  it  reaches  a  pasty  state 
the  charge  is  rolled  into  balls,  called  puddle  balls,  that  average  about 
150  pounds  apiece.  From  the  puddle  furnace  these  balls  are  taken  to 
a  rotary  squeezer  that  kneads  and  squeezes  out  a  large  amount  of  slag 
or  they  are  taken  to  a  drop  hammer  where  the  slag  is  hammered  out. 
The  balls  are  then  rolled  into  bars,  which  removes  more  of  the  slag, 
leaving  the  rolled  bars  containing  from  1  to  2%.  These  flat  bars  are  then 
cut  up  into  short  lengths  and  form  the  muck  bar  used  in  making  crucible 
steel. 

Sometimes  in  this  country  and  as  a  general  thing  in  Europe,  the 
squeezer  is  not  used,  in  which  case  the  puddle  ball  is  worked  under  a 
hammer  or  " shingled"  to  remove  the  slag,  and  weld  the  particles  of  iron 
in  the  ball  together.  Puddling  and  shingling  being  extremely  hard  and 
hot  work,  however,  efforts  are  continually  being  made  to  devise  machines 
that  will  do  the  work.  The  rotary  squeezer  does  that  part  of  the  work 


CRUCIBLE    PROCESS   OF   STEEL   MAKING  41 

cheaper  than  it  can  be  done  by  hand  labor,  and  many  different  kinds 
of  automatic  puddling  furnaces  have  been  designed  and  built.  With 
these  latter  the  finished  product  has  not  been  turned  out  as  good,  as  yet, 
as  it  can  be  made  by  hand  labor.  The  results  obtained,  however,  with 
the  mechanical  furnace,  have  nearly  reached  those  desired,  and  may  yet 
be  made  satisfactory. 


CHAPTER  V 
ELECTRIC  FURNACES  FOR  STEEL  MAKING 

THE  electric  furnace  has  been  brought  into  quite  prominent  use  in 
the  last,  few  years  for  the  making  of  steel.  In  certain  ways  it  has 
proved  itself  to  be  a  commercial  success,  while  in  others  it  is  still  in  the 
experimental  stage,  but  from  the  present  progress  (1910)  in  the  art 
it  would  look  as  though  the  electric  furnace  was  destined  to  supplant 
the  expensive  crucible  method  of  steel  making,  and  if  electricity  could 
be  obtained  cheap  enough  it  might  even  be  a  strong  competitor  to  the 
open-hearth  method. 

When  a  good  ore  can  be  procured  the  electric  furnace  can  produce 
a  metal  with  a  higher  degree  of  purity  than  any  of  the  other  processes, 
owing  to  the  absence  of  sulphurous  and  oxidizing  gases.  Mr.  Harbord, 
the  Canadian  government  expert,  said,  "Steel  equal  in  all  respects  to  the 
best  high-grade  Sheffield  crucible  steel  can  be  produced  in  the  electric 
furnace  at  a  less  cost  than  by  the  ordinary  crucible  methods." 

Owing  to  the  extremely  high  temperature  available  a  more  perfect 
elimination  of  the  detrimental  metalloids  can  be  secured  and  because  of 
the  neutral  or  reducing  atmosphere  it  is  possible  to  secure  a  more  per- 
fect deoxidation.  It  cannot  remove  arsenic  and  copper,  but  it  practically 
eliminates  phosphorus  and  sulphur,  and  thus  removes  the  injurious  effects 
of  these.  The  sulphur  is  oxidized  out  until  only  a  trace  is  left  and  the 
phosphorus  remains  in  the  metal  only  in  very  small  percentages.  For 
the  high-grade  steels  such  as  tungsten,  nickel-chrome,  self-hardening 
and  high-speed  tool,  which  are  made  out  of  blast-furnace  products  and 
scrap  it  has  given  good  satisfaction  in  several  steel  plants  in  Germany, 
France,  Sweden,  and  Italy. 

STASSANO   REVOLVING   FURNACES 

In  the  Stassano  furnaces,  shown  in  Fig.  31,  that  are  being  operated  in 
Turin,  Italy,  the  heat  is  generated  by  three  electrodes  which  come  together 
in  the  center  of  an  enclosed  furnace  immediately  over  the  metal.  This 
furnace  is  also  mechanically  revolved  in  order  to  agitate  the  metal  and 
thus  accelerate  the  chemical  reaction  and  reduce  the  time  of  operation 
to  a  minimum.  It  is  also  built  without  the  revolving  mechanism  for 
some  uses. 

42 


ELECTRIC  FURNACES  FOR  STEEL  MAKING  43 

The  electrodes  are  cooled  by  water-jackets  that  surround  them  on 
the  outside  of  the  furnace,  and  the  cylindrical  melting  chamber  is 
enclosed  so  that  the  atmosphere  throughout  it  will  be  neutral.  The 


FIG.  31.  —  Stassano  revolving 
electric  furnace. 

material  treated  is  not  in  contact  with  the  electrodes  or  other  material, 
and  therefore  its  composition  is  not  subjected  to  any  alteration,  as  the 
furnace  only  furnishes  the  heat  to  produce  the  reaction  between  the 
substances  in  the  charge,  and  does  not  introduce  other  elements. 


44 


COMPOSITION  AND   HEAT-TREATMENT   OF   STEEL 


ELECTRIC   FURNACES   FOR   STEEL   MAKING  45 

Among  the  different  oxides  contained  in  commercial  iron  ore  that  of 
iron  is  the  first  one  which  is  reduced.  The  remaining  oxides  (SO3,  MnO, 
MnO2,  CaO,  MgO,  etc.)  are,  therefore,  left  unreduced  and  are  forced 
to  pass,  with  the  assistance  of  a  flux,  into  the  slag.  In  the  same  way, 
if  pig  iron  or  iron  scrap  is  used,  mixed  with  slag-forming  materials,  the 
pig  iron  and  impure  iron  may  be  successfully  refined  in  the  same  furnace, 
and  this  is  accomplished  by  starting  from  predetermined  quantities  with- 
out any  tests  during  the  process. 

When  refining  pig  iron  or  impure  iron,  oxide  of  iron  must  be  added, 
which  may  be  natural  or  artificial  (hammerslag)  or  powder  of  rusty  scrap. 
To  make  the  slag,  the  common  fluxes,  used  in  metallurgy,  are  suitable 
and  may  be  selected  according  to  convenience  and  special  requirements. 
Since  the  atmosphere  in  the  furnace  is  chemically  neutral  and  the  oper- 
ation can  be  carried  out  for  any  length  of  time  desired,  the  metal  can 
be  freed  almost  entirely  from  its  impurities  without  the  risk  of  harmful 
oxidation. 

Refined  iron  may  be  obtained  direct  from  the  ore  in  this  furnace  if 
it  is  charged  with  iron  ore  mixed  with  a  reducing  agent  and  the  proper 
fluxes,  in  the  correct  proportions,  to  transform  the  gangue  into  a  slag  of 
a  composition  that  will  absorb  the  impurities  in  a  single  operation.  Such 
a  charge,  being  gradually  heated  with  the  exclusion  of  air,  cannot  absorb 
oxygen  from  it,  and  the  flux  maintains  its  quality  at  a  rising  temperature 
so  that  it  is  able  to  perform  its  mission  when  the  right  temperature  has 
been  reached. 


HEROULT  FURNACE 

The  Heroult  furnace,  as  shown  in  Fig.  32,  is  but  a  modified  open- 
hearth,  with  the  heat  introduced  above  the  metal  by  the  electric  current 
in  place  of  gas;  no  electrical  parts  being  in  the  furnace  proper.  Thus 
the  bottom  and  side  can  be  patched  as  fast  as  they  may  be  burned  away 
without  interfering  with  the  work  of  the  furnace. 

In  the  later  types  of  Heroult  furnace  the  heat  is  introduced  by  means 
of  two  electrodes  working  in  series;  the  current  passing  through  the  bath 
from  one  electrode  to  another,  and  vice-versa.  The  power  being  the 
same  in  both  cases,  this  necessitates  carrying  only  one  half  the  current 
that  would  be  needed  if  the  current  flowed  from  one  electrode  through 
the  bath,  and  thence  through  a  plate  contact,  in  the  bottom  of  the  furnace, 
as  shown  in  Fig.  33. 

In  this  case  the  heat  is  generated  in  the  slag  and  not  in  the  metal 
itself;  thus  making  the  slag  the  hottest  part  of  the  furnace,  so  that  all 


46 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


impurities  can  be  removed  by  the  use  of  special  slags.  The  poorest  kind 
of  scrap  can  therefore  be  used,  as  the  sulphur  and  phosphorus  are  both 
removed  at  a  low  cost,  and  the  metal  can  be  converted  into  the  finest 
grade  of  tool  steel. 

In  a  5-ton  furnace  starting  on  cold  materials  one  ton  of  metal  can 
be  melted  and  partially  refined,  with  600  kilowatt-hours;  for  the  finish- 


FIG.  33.  —  Heroult  resistance  furnace. 

ing  slag  100  more  would  be  necessary,  making  700  kilowatt-hours  all 
told.  In  a  15-ton  furnace  these  figures  would  be  considerably  reduced. 
If  molten  metal  is  charged  into  the  5-ton  furnace  and  this  only  needs  to 
be  deoxidized,  desulphurized,  and  recarburized,  it  will  take  from  140 
to  160  kilowatt-hours,  and  for  a  15-ton  furnace  this  would  probably 
be  cut  down  to  about  100  kilowatt-hours.  In  cold  melting  and  continu- 
ous work  the  consumption  of  electrodes  is  from  60  to  65  pounds  for  each 


ELECTRIC  FURNACES  FOR  STEEL  MAKING  47 

ton  of  steel,  which  includes  the  waste  ends  of  the  electrodes.  When  molten 
metal  is  charged  into  the  furnace,  this  consumption  is  only  from  10  to 
15  pounds  per  ton  of  steel.  The  electrodes  just  touch  the  flux  covering 
the  molten  metal  and  can  be  operated  automatically  or  by  hand. 

About  the  best  lining  for  this  furnace  is  good  magnesite  mixed  with 
basic  slag,  with  tar  for  a  binder;  burnt  dolomite  can  also  be  used  success- 
fully. The  furnace  can  be  lined/  by  any  one  who  can  make  a  good  bottom 
in  a  basic  open-hearth  furnace.  The  lining  is  never  exposed  to  silicious 
slags,  and  can  be  repaired  after  each  heat  by  simply  throwing  in  mag- 
nesite or  dolomite,  as  the  case  may  be.  This  should  make  it  last  a  long 
time,  and  with  the  furnace  run  with  due  care,  one  year  is  not  too  long 
for  it  to  last,  although  furnaces  have  had  to  be  relined  in  three  months. 
The  roof  is  damaged  the  most,  and  this  usually  has  to  be  replaced  once 
a  month.  For  that  reason  an  extra  roof  is  kept  on  hand  so  the  change 
can  be  made  in  a  few  hours. 

Two  15-ton  Heroult  furnaces  are  now  being  used  by  the  United  States 
Steel  Corporation  (August,  1910),  and  this  is  about  the  largest  size  that 
can  be  successfully  operated  when  two  slags  are  used,  owing  to  the  difficul- 
ties that  might  be  encountered  in  raking  the  first  slag  off  the  molten  metal. 
The  first  slag  used  being  an  oxidizing  one  to  remove  the  phosphorus,  and  the 
second  deoxidizing  for  the  removal  of  the  sulphur  and  the  gases.  It  is  the 
intention  to  build  30-ton  furnaces,  however,  where  only  one  slag  is  used. 

The  detrimental  features  of  this  style  of  furnace,  which  are  yet  to 
be  overcome,  are  the  high  electrode  costs,  and  the  possibility  of  increasing 
the  carbon  contents  of  the  finished  metal.  For  melting  purposes  as  in 
steel  foundry  work  it  is  also  difficult  to  choose  a  suitable  protective  flux, 
that  will  act  as  a  heating  medium,  and  still  not  act  on  the  ingredients  of 
the  molten  metal. 

KELLER    FURNACE 

The  Keller  furnaces  are  more  or  less  of  the  Heroult  type,  but  differ 
in  constructional  details.  These  are  shown  by  Fig.  34,  which  is  a  sec- 
tional elevation.  As  will  be  seen,  the  carbon  electrodes  A«are  massive 
and  are  lowered  into  vertical  shafts  that  are  separated  but  connected  below 
by  a  lateral  canal  B.  The  electrodes  are  surrounded  by  the  raw  material 
in  these  vertical  shafts,  and  the  electrical  current  passes  from  one  elec- 
trode to  the  other,  down  through  this  material  and  through  the  lateral 
canal,  in  which  it  becomes  molten.  The  molten  metal  is  then  drawn  off 
by  tapping.  A  central  electrode  is  located  at  C.  This  furnace  is  well 
adapted  for  making  steel  castings,  and  it  can  be  cleaned  by  dumping  the 
bottom  D.  When  thus  used  a  central  stack  is  added  to  the  furnace 
shown,  that  feeds  the  raw  material  into  the  vertical  shafts  surrounding 
the  electrodes. 


48  COMPOSITION   AND  HEAT-TREATMENT  OF  STEEL 


FIG.  34.  —  Keller  electric  steel  furnace. 


ELECTRIC   FURNACES  FOR  STEEL   MAKING 

KJELLIN   AND    COLBY    FURNACES 


49 


Resistance  furnaces  of  the  induction  type  were  invented  by  Mr. 
E.  A.  Colby,  in  the  United  States  in  1887,  and  independently  reinvented 
by  Dr.  Kjellin  in  Sweden  twelve  years  later.  As  a  natural  sequence  a 
combination  was  formed  and  the  patents  of  both  are  used  on  the  same 
furnaces. 

In  Fig.  35  is  shown  the  principle  on  which  this  simple  induction  fur- 
nace is  built.  It  is  in  reality  a  transformer,  in  which  the  bath  of  molten 


FIG.  35.  —  Kjellin  induction  furnace. 

metal  forms  the  secondary  circuit.  The  magnetic  circuit  C  is  built  up 
of  laminated  sheet  iron  like  the  core  of  a  transformer.  The  primary  cir- 
cuit is  a  coil  D,  consisting  of  a  number  of  turns  of  insulated  copper  wire 
or  tubing  surrounding  the  magnetic  circuit.  The  ring-shaped  crucible 
A,  made  of  suitable  refractory  materials,  also  surrounds  the  magnetic 
circuit,  and  when  filled  with  molten  metal  forms  the  secondary  circuit 
of  the  transformer.  The  annular  crucible  is  supplied  with  cover  K. 
When  the  coil  D  is  connected  with  the  poles  of  an  alternating-current 


50  COMPOSITION  AND   HEAT-TREATMENT  OF   STEEL 

generator,  the  current,  when  passing  through  the  coil,  excites  a  varying 
magnetic  flux  in  the  iron  core  and  the  variation  in  the  magnetic  flux  induces 
a  current  in  the  closed  circuit  formed  by  the  molten  metal  in  the  crucible 
A.  The  ratio  between  the  primary  and  secondary  current  is  fixed  by  the 
number  of  turns  of  the  primary,  and  the  magnitude  of  the  current  in  the 
steel  is  then  almost  the  same  as  the  primary  current  multiplied  by  the 
turns  of  the  primary  coil.  Thus,  in  a  small  furnace  of  this  type  a  current 
of  500  volts  and  280  amperes  supplied  to  D  induces  a  current  of  seven 
volts  and  20,000  amperes  in  the  metallic  bath. 

In  this  style  of  furnace  the  charge  may  be  either  in  the  hot  molten 
state  or  in  the  form  of  cold  scrap,  pig  iron,. etc.  When  the  latter  materials 
are  charged  one  or  more  metal  rings,  made  of  cast  iron,  wrought  iron,  or 
steel,  must  be  placed  in  the  hearth  A  to  complete  the  electrical  circuit 
and  start  the  melting.  When  molten  metal  is  charged,  this  of  itself 
forms  the  circuit,  and  for  continuous  working  it  is  customary  to  leave  a 
sufficient  amount  of  metal  in  the  crucible  A  to  establish  the  bath. 

If  the  charge  is  made  with  molten  metal  a  saving  in  time  and  power 
is  effected  in  refining  the  bath.  When  scrap  and  pig  iron  is  charged, 
the  metal  ring  must  be  put  in  and  the  current  turned  on  until  this  is  melted 
down.  The  charge  is  then  gradually  added  and  melted  until  the  full 
charge  is  obtained.  After  this  the  temperature  is  raised  to  any  desired 
point  and  the  necessary  additions  made  to  give  the  required  percentages 
of  carbon,  manganese,  nickel,  chrome,  tungsten,  etc.,  according  to  the 
kind  of  steel  that  is  to  be  produced. 

This  is  primarily  a  melting  furnace,  and  the  best  results  are  obtained 
in  melting  high-grade  materials.  As  a  commercial  substitute  for  the 
crucible  method  it  has  several  advantages:  High  and  easily  controlled 
temperatures  are  attainable,  as  the  temperature  is  directly  dependent 
upon  the  primary  circuit;  the  process  is  clean  and  gases  cannot  attack  and 
injure  the  bath;  "overkilling"  is  practically  impossible  and  a  saving  in 
labor  is  effected.  A  furnace  that  will  produce  1000  tons  of  steel  per  year 
can  be  easily  handled  by  three  men  and  a  boy  per  shift. 

A  Kjellin  induction  furnace  is  shown  in  Fig.  36,  as  it  is  tapping  1000 
pounds  of  tool  steel  into  a  ladle  for  pouring  into  ingot  molds.  This  fur- 
nace is  hung  in  a  frame  on  trunnions,  and  is  tilted  when  it  is  necessary 
to  pour  off  the  heat,  by  the  aid  of  gears,  electrically  operated  by  a 
switch  from  the  furnace  platform. 

One  of  the  difficulties  encountered  with  furnaces  of  this  style,  the 
hearth  of  which  is  in  the  shape  of  an  annular  ring,  is  caused  from  what 
is  commonly  known  as  the  " pinch"  phenomena.  When  an  alternating 
or  direct  current  passes  through  a  liquid  conductor,  the  electromagnetic 
forces  tend  to  contract  that  conductor  in  cross-section.  This  contrac- 
tion is  apt  to  localize  itself  at  some  certain  spot  and  form  a  depression 


ELECTRIC  FURNACES  FOR  STEEL  MAKING  51 

in  the  molten  metal  that  gives  it  the  appearance  of  being  pinched  by  an 
invisible  force. 

This  force  is  a  function  of  the  current,  and  size  and  shape  of  the  cross- 
section  of  molten  metal,  and  is  independent  of  the  resistance,  voltage, 
watts,  temperature,  heat,  length  of  channel,  etc.,  except  where  changes 
in  these  effect  the  other  quantities.  Involved  in  the  actual  contraction 
is  also  the  smoothness  of  channel,  viscosity,  fluid  friction,  weight  of  float- 
ing masses,  etc. 

The  contracting  force  is  small  for  a  current  with  relatively  low  den- 


FIG.  36.  —  Kjellin  induction  furnace  tapping  1000  pounds 
of  tool  steel. 

sities,  but  when  these  become  higher  the  force  is  great  enough  to  contract 
the  cross-section  of  molten  metal  to  zero  and  thus  rupture  the  circuit. 
When  increasing  currents  are  small  the  level  falls  slowly  at  first  and  then 
more  rapidly.  When  a  certain  unstable  level  is  reached  the  contraction 
becomes  very  rapid  for  the  same  increments  of  current.  There  is  also 
a  certain  critical  current  at  which  rupture  might  take  place  immediately. 
Into  the  depression  formed  is  liable  to  drift  the  more  refractory,  solid, 
floating  materials  that  will  prevent  a  reunion  of  the  molten  metal  and 
cause  a  freezing  of  the  charge  before  they  can  be  removed.  When  this 


52 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


ELECTRIC  FURNACES  FOR  STEEL  MAKING  53 

occurs  it  is  difficult  to  start  the  current  flowing  again  so  as  to  melt  the 
metal,  and  the  furnace  usually  has  to  be  taken  apart  and  rebuilt. 

The  "pinch"  need  not  be  feared  in  low  current  density  furnaces, 
except  when  other  causes  might  produce  local  contraction,  as  it  only 
takes  place  at  relatively  high  current  densities.  But  when  it  does  occur 
it  means  a  frozen  charge  or  a  broken  core,  unless  the  separated  metal 
can  be  quickly  brought  together  by  opening  the  external  circuit  for  an 
instant  and  then  follow  it  by  a  reduce  current. 

A  positive  limit,  above  which  the  current  and  thus  the  temperature 
cannot  go,  is  fixed  by  the  critical  current.  This  limit  is  greater  with  a 
greater  density,  lesser  viscosity,  deeper  channel,  more  regular  and  smoother 
channel,  and  a  molten  metal  surface  that  is  freer  from  heavy  floating 
masses. 

ROCHLING-RODENHAUSER   ELECTRIC    FURNACE 

The  Rochling-Rodenhauser  furnaces,  of  which  one  of  the  8-ton 
furnaces  is  shown  in  Fig.  37,  consists-  of  the  same  arrangement  of  trans- 
former and  primary  coils  as  is  shown  in  the  Kjellin  furnace.  In  addition, 
however,  it  has  a  number  of  steel  terminal  plates  embedded  in  the  lining 
and  these  are  connected  to  a  few  heavy  turns  of  copper,  placed  outside 
the  primary  coils,  that  collect  and  feed  the  induced  current  in  these  turns 
to  the  terminal  plates. 

These  are,  therefore,  termed  combination  furnaces,  and  are  designed 
to  suppress  the  magnetic  leakage  that  would  occur  in  large  furnaces  of 
the  simple  induction  type;  the  auxiliary  turns  being  located  in  close  prox- 
imity to  the  primary  coil  and  magnet  core.  The  total  result  is  that  the 
main  hearth  can  be  made  of  much  larger  cross-section,  and  a  good  power 
factor  can  be  obtained  even  in  big  furnaces  without  the  use  of  a  current 
of  such  low  periodicity  as  was  necessary  with  the  original  induction  fur- 
naces. 

This  furnace  is  built  for  single-phase  or  three-phase  currents;  the  three 
phase  being  more  suitable  for  large  quantities  of  metal  and  for  large  daily 
outputs  at  a  normal  periodicity.  The  principles  on  which  these  furnaces 
are  built  can  be  seen  in  Figs.  38  and  39. 

In  Fig.  38,  H  H  are  the  two  legs  of  the  iron  core  of  the  transformer. 
They  are  surrounded  by  primary  coils  .4,  connected  with  the  alternating- 
current  generator.  Through  the  action  of  the  currents  in  the  primary 
coils,  secondary  currents  are  induced  in  the  two  closed  circuits  formed 
by  the  bath;  these  two  circuits  being  connected  so  that  the  whole  looks 
like  the  figure  8.  The  primary  coils  are  so  arranged  that  the  induced 
currents  in  the  common  part  of  the  two  circuits,  that  is,  between  the 
legs  H  H  of  the  iron  core,  have  the  same  direction. 

So  far  the  furnace  acts  like  two  combined  ordinary  induction  furnaces. 


54  COMPOSITION^  AND  HEAT-TREATMENT  OF  STEEL 

The  difference  consists  in  the  use  of  extra  secondary  coils  B  B,  surround- 
ing the  primary  coils  A  A.  From  these  secondary  coils  the  currents 
are  conducted  to  metallic  plates  E.  The  plates  are  covered  by  an  elec- 


c-d 


FIG.  38.  —  Outline  sections  of  single  phase.     Combination  furnace. 

trically  conducting  mixture  of   refractory  material  G,  that  forms   part 
of  the  lining  of  the  furnace. 

The  currents  from  the  secondaries  pass  from  the  plates  E,  through 


ELECTRIC  FURNACES  FOR  STEEL  MAKING 


55 


the  lining  G,  and  then  through  the  main  hearth  D  of  the  furnace.  The 
channels  C  only  act  as  conductors  for  the  secondary  currents  induced 
in  the  bath.  In  the  main  hearth  D  we  thus  have  the  currents  from  the 
channels  C  C,  and  also  from  the  extra  secondaries  B  B. 

The  construction  of  the  three-phase  furnace  is  practically  the  same 
as  that  of  the  single-phase,  except  that  a  third  transformer  is  added  and 
therefore  only  a  plan  view  is  shown  in  Fig.  39. 

The  amount  of  extra  power  that  can  be  given  to  the  furnace  by  means 
of  the  extra  coils  is  of  course  not  unlimited,  because  increased  power 
means  increased  current,  and  consequently  increased  current  density 


FIG.  39.  —  Plan  view  of  3-phase  furnace. 

in  that  part  of  the  lining  that  conducts  the  current  to  the  steel.  This 
current  density  must  not  be  driven  too  far,  because  the  heat  evolved  when 
the  current  passes  the  lining  will  increase  as  the  square  of  the  current, 
and  too  high  a  current  density  would  therefore  result  in  the  destruction 
of  the  lining. 

This  is  the  reason  why  a  combination  of  induced  currents  and  currents 
taken  from  the  extra  coils  must  be  used.  It  would  not,  for  the  reason 
stated,  be  possible  to  conduct  all  the  amount  of  current  through  the 
lining  that  is  necessary  for  the  working  of  the  furnace,  not  to  speak  of 
the  pinching  effect  that  would  very  probably  cut  off  the  current  at  the 
contact  between  the  steel  and  the  lining,  if  the  current  density  in  the 
lining  were  driven  too  far. 


56  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

The  Rochling-Rodenhauser  furnace  was  designed  for  refining  fluid 
Bessemer  steel  from  the  converter,  in  order  to  produce  a  higher  quality 
of  steel  rails  than  before,  and  also  with  the  intention  of  making  high- 
class  steel  in  general. 

For  refining  purposes  the  furnace  is  worked  in  the  following  manner: 

After  tapping,  fluid  steel,  from  the  converters,  is  poured  into  the  fur- 
nace, and  suitable  materials  —  burnt  limestone  and  mill  scale  —  for 
forming  a  dephosphorizing  basic  slag  are  added.  When  the  reactions 
are  ended  this  slag  is  taken  off  by  tilting  the  furnace.  For  making  rails 
the  phosphorus  is  brought  down  sufficiently  low  in  one  operation,  but 
for  the  making  of  the  highest  class  of  steel  the  operation  has  to  be  repeated. 

When  the  phosphorus  is  removed,  the  carbon  in  the  steel  (if  carbon 
steel  is  made)  is  adjusted  by  adding  pure  carbon  to  the  bath,  and  after- 
wards a  new  basic  slag  is  formed  in  order  to  remove  the  sulphur.  This 
slag  is  also  formed  of  burnt  lime,  sometimes  with  the  addition  of  fluxes 
such  as  fluorspar. 

One  necessary  condition  for  successful  desulphuration  is  that  the 
slag  be  free  from  iron,  and  therefore  sometimes  ferro-silicon  is  added  in 
order  to  quicken  the  reduction  of  the  iron  in  the  slag.  How  far  this 
refining  will  have  to  be  carried  naturally  depends  on  the  quality  of  steel 
wanted.  By  repeated  refining  operation  with  fresh  slag,  the  phosphorus 
and  sulphur  can  be  brought  down  to  an  exceedingly  low  percentage,  but 
this  refining,  of  course,  takes  a  longer  time  and  consequently  more  electric 
energy  per  ton  of  finished  product. 

GIROD    ELECTRIC    STEEL   FURNACE 

From  the  numerous  experiments  that  have  been  carried  on,  has  been 
deduced  the  fact  that  the  best  method  of  insuring  practical  success  in 
the  operation  of  electrical  furnaces  is  to  so  design  them  that  they  will 
have  the  utmost  simplicity  in  the  construction  of  the  necessary  apparatus. 
Until  the  Girod  furnace  was  perfected  the  Heroult  was  the  simplest  and 
to  this  was  due  its  success,  but  now  (June,  1910)  the  Girod  heads  the 
list  of  electrode  furnaces  in  simplicity  and  safety  in  construction  and 
operation. 

The  owners  of  the  process  are  ready  to  guarantee  the  successful  work- 
ing commercially  of  a  25-ton  furnace  for  refining  steel  previously  made 
molten  in  an  open-hearth  furnace.  While  this  is  a  cheaper  method  of  pro- 
ducing a  good  grade  of  steel  than  that  of  melting  down  the  raw  materials 
in  the  electric  furnace  and  then  refining  it,  Mr.  Paul  Girod,  the  inventor 
of  this  furnace,  claims  that  steel  cannot  be  produced  from  a  molten 
charge  that  has  the  same  good  qualities  as  that  made  exclusively  in  the 
electric  furnace  from  pig  iron,  scrap,  etc.  Such  qualities,  for  instance, 


ELECTRIC  FURNACES  FOR  STEEL  MAKING 


57 


58 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


as  resistance  to  shock;  and  in  tool  steels,  hardness,  tenacity,  and  durability 
after  hardening.     In  this  Mr.  Girod  is  supported  by  others. 

In  Fig.  40  is  shown  a  12-ton  Girod  furnace  as  it  is  pouring  the  charge 
into  a  ladle  by  tilting.  To  the  right  of  this  will  be  seen  another  furnace; 
the  picture  being  taken  at  the  steel  works  started  by  Mr.  Girod  a  few 
years  ago  in  Ugine,  Savoie,  France.  This  company  has  a  good  water- 


FIG.  41.  —  Plan  and  sectional  elevation  of  12-ton  Girod  electrical  furnace. 

power  for  generating  their  electricity,  and  are  to-day  (June,  1910) 
operating  19  electric  furnaces,  with  from  400  to  600  electrical  horse-power 
each,  while  12  new  furnaces  are  being  constructed  that  will  consume  1200 
horse-power  each.  All  kinds  of  steel  are  being  made,  from  structural 
up  to  high-speed  tool  steel. 

The  construction  of  this  furnace  can  be  seen  by  a  study  of  Fig.  41. 


UNIVERSITY 

OF 
•4 LI  FOR  1 


C  FURNACES  FOR  STEEL  MAKING 


59 


While  it  is  classed  with  the  electrode  furnaces  it  is  in  reality  a  combination 
of  the  resistance  and  arc  heating  and  seems  to  work  as  well  in  large  units 
as  in  small  ones.  One  or  more  electrodes  A  according  to  the  size  of  the 
furnace,  are  lowered  through  a  hole,  or  holes,  in  the  cover  that  is  lined 
with  silica  brick,  and  the  metal  M,  which  is  from  12  to  14  inches  deep, 
serves  as  the  opposite  electrode.  The  current  passes  from  electrode 
A,  in  the  form  of  an  arc,  into  the  slag  S,  where  a  large  amount  of  heat 
is  produced,  then  into  the  metal  M,  and  finally  out  through  the  contact 
pieces  C  to  the  current  conductor.  If  a  number  of  electrodes  are  used 
above  the  bath  they  are  in  parallel. 

The  most  important  principle  in  the  Girod  process  is  the  effective 


FIG.  41a.  —  Operating  principle  of  Girod  furnace. 

manner  in  which  the  electric  current  is  made  to  pass  through  the  molten 
metallic  body  and  cause  it  to  become  an  important  heat  producer. 

Water  is  driven  through  a  passage  about  6  inches  deep  in  the  outer 
end  of  each  contact  piece  C,  so  as  to  cool  them  and  aid  in  regulating 
their  temperature  and  resistance.  The  length  and  cross-section  of  the 
contact  pieces  are  such  that  each  will  take  up  only  a  certain  part  of  the 
whole  current  and  thus  none  become  overheated  and  greatly  increase 
in  resistance.  They  are  made  of  pure  iron  to  avoid  any  deterioration 
of  the  furnace  charge,  and  are  not  only  connecting  rods  between  the 
furnace  charge  and  the  current  generators,  but  also  serve  as  regulating 
current  distributors,  by  making  the  electric  current  pass  uniformly  from 


60  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

and  to  the  centrally  hanging  carbon  rod  or  rods  in  radial  direction  to 
and  from  the  periphery  of  the  bath.  This  is  important,  not  only  for 
uniformly  heating  the  bath,  but  also  for  keeping  every  part  of  the  liquid 
metal  in  constant  motion.  This  movement  accelerates  the  contact 
between  the  impurities  of  the  iron  and  the  refining  slag  swimming  on 
top  of  the  bath. 

In  operating  on  cold  materials  the  electrode  is  lowered  until  it  rests 
upon  the  heap  of  scrap;  then  the  current  finds  no  other  way  out  than  by 
means  of  numerous  small  arcs  through  the  whole  mass  of  material,  thus 
breaking  it  down  simultaneously  in  all  parts  of  the  hearth,  with  no  stick- 
ing of  cold  pieces  to  the  bottom.  When  feeding  cold  scrap  one  does  not 
put  in  the  whole  charge  at  once.  After  the  larger  part  of  the  charge  has 
been  deposited  upon  the  hearth,  the  current  is  sent  through  the  heap 
as  described;  then  the  rest  of  the  charge  is  put  into  the  furnace,  together 
with  the  first  batch  of  the  refining  ingredients.  Taking  the  run  of  a 
2-ton  furnace  as  an  example,  the  charge  consists  of  4500  to  5500  pounds 
of  iron  scrap,  and  the  first  batch  of  refining  slag  usually  consists  of  about 
175  pounds  of  lime  (CaO)  and  500  pounds  of  iron  oxide  ore.  Together 
with  the  iron  oxide  that  covers  the  scrap,  the  iron  ore  serves  as  an  oxidi- 
zing agent. 

The  smelting  of  the  iron  charge  and  the  first  batch  of  refining  slag 
requires  IJ  to  5  hours.  As  the  slag  becomes  exhausted  of  iron  oxide 
and  therefore  of  its  oxidizing  power,  samples  are  taken  and  tested  to 
ascertain  the  degree  of  refinement  of  the  molten  metal.  According  to  the 
degree  of  purification,  the  furnace  now  receives  (after  the  first  slag  has 
been  skimmed  off)  a  second,  and  if  necessary  a  third  batch  of  lime-iron- 
oxide  slag.  After  the  removal  of  the  last  slag  the  surface  of  the  metal 
bath  is  thoroughly  cleansed  by  throwing  in  about  75  pounds  of  lime  and 
skimming  this  off  after  a  while.  The  further  treatment  of  the  bath  depends 
upon  the  impurities  which  could  not  be  removed  by  the  lime-iron-oxide 
refining,  and  upon  the  quality  of  steel  to  be  produced.  Thus  deoxidizing 
or  other  refining  agents  are  employed;  such  as,  ferro-mangano-silicon, 
ferro-aluminium-silicon,  ferro-mangano-aluminium-silicon,  and  other  alloys. 

The  final  step  in  the  production  of  special  steels  is  the  addition  of 
iron  alloyed  with  metals  like  nickel,  tungsten,  chromium,  and  others,  after 
these  refining  operations. 

A  removable  cast-iron  frame  is  fitted  to  the  cover,  and  this  contains 
water-jacketed  ports  through  which  the  electrodes  enter  the  furnace. 
While  the  metallic  frame  is  not  necessary  it  serves  a  useful  purpose  by 
stiffening  the  cover  and  keeping  air  from  entering  the  furnace  and  attack- 
ing the  bath.  As  the  electrodes  have  the  same  polaritj',  when  more  than 
one  is  used,  there  is  no  danger  of  short  circuits  through  the  metal  frame 
and  collars  and  across  the  cover.  The  electrodes  are  easily  regulated 


ELECTRIC   FURNACES  FOR  STEEL  MAKING  61 

automatically  by  feeding  from  the  generator,  on  the  voltage,  in  the  single 
electrode  furnaces,  or  on  the  intensity  of  the  current  when  this  is  fed  by 
a  transformer,  or  several  electrodes  are  supplying  current  equally.  The 
electrode  consumption  is  about  38  pounds  in  2-ton,  and  31  pounds  in 
12-ton,  furnaces  per  ton  of  steel  produced. 

Two  2J-ton  Girod  furnaces  that  are  in  use  in  France  and  Belgium, 
are  shown  in  Fig.  42.  One  of  this  style  is  used  in  Switzerland  for  steel 
castings  only. 

SUMMARY 

Many  others  have  been  and  are  experimenting  with  electric  furnaces 
in  the  hope  of  improving  them  and  cheapening  their  operation,  among 
which  might  be  mentioned  Gustave  Gin,  Marcus  Ruthenburg,  E.  A. 
Greene,  F.  S.  McGregory,  Prof.  B.  Igewsky,  and  others,  but  none  of 
these  have  as  yet  passed  the  experimental  stage,  and  been  put  to  prac- 
tical use.  Horace  W.  Lash,  of  Cleveland,  Ohio,  U.  S.  A.,  has  developed 
a  process  that  is  applicable  to  the  electric  furnace,  but  as  it  is  also  appli- 
cable to  the  open-hearth  process  it  cannot  be  classed  with  the  purely  elec- 
tric steels. 

Some  years  ago  Mr.  Lash  became  interested  in  the  direct  production 
of  steel  from  the  ore,  and  made  experiments.  The  outcome  of  this  was 
a  compromise  between  the  direct  and  refining  methods.  He  found  that 
when  an  intimate  mixture  of  iron  ore,  carbon,  fluxes,  and  cast-iron  borings 
was  heated,  a  reduction  took  place;  by  proportioning  the  mixture  properly, 
steel  of  the  desired  grade  could  be  produced  and  practically  the  whole 
of  the  iron  in  the  mixture  recovered  as  good  steel. 

A  typical  Lash  mixture  is  as  follows:  Granulated  pig  iron,  or  cast- 
iron  borings,  23%;  iron  ore,  60%;  coke,  11%;  lime,  6%.  To  reduce  this 
in  the  open -hearth  furnace  required  the  addition  of  pig  iron  or  scrap. 
A  typical  charge  for  100  tons  of  steel  ingots  being:  Lash  mixture,  122 
tons;  pig  iron,  32  tons;  ore,  2  tons.  In  the  electric  furnace  pig  iron  or 
scrap  is  not  necessary,  and  for  100  tons  of  steel  ingots  the  charge  would 
be,  Lash  mixture,  172  tons;  ore,  2  tons. 

The  experiments  proved  that  a  superior  quality  of  steel  was  obtained; 
the  cost  of  its  production  was  in  general  lower  than  when  the  regular 
methods  of  making  steel  were  used;  and  that  the  electric  furnace  was 
the  best  method  for  the  process.  Companies  have  been  organized  in 
Cleveland  and  Canada  for  making  steel  by  the  Lash  process. 

That  the  electric  furnace  will  produce  as  high,  if  not  a  higher,  grade 
of  steel  than  is  produced  by  any  of  the  other  methods  has  been  fully 
established;  that  it  is  cheaper  than  the  crucible  process,  and  may  in  time 
equal  the  open-hearth,  is  also  pretty  well  recognized.  That  magnetite 
and  hematite  ores  can  be  economically  smelted;  that  sulphur  and  phos- 
phorus can  be  reduced  to  a  few  thousandths  of  a  per  cent,  even  without 


62 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


manganese;  that  the  percentage  of  silicon  can  be  altered  at  will,  and  that 
ores  containing  titanic  acid  up  to  5%  can  be  reduced  in  the  electric  furnace, 
make  of  it  one  of  the  coming  factors  in  the  manufacture  of  steel. 


FIG.  42.  —  2i  ton  Girod  furnaces  in  use  in  France  and  Belgium. 

In  two  steels  of  the  same  composition,  1  inch  square,  one  of  which 
was  made  in  the  electric  furnace  and  the  other  in  a  crucible,  a  considerable 
difference  in  torsion  was  noted.  The  electric  steel  was  twisted  cold  until 
it  looked  like  a  corkscrew;  while  the  crucible  steel  only  took  half  as  many 


ELECTRIC  FURNACES  FOR  STEEL  MAKING  63 

twists  before  breaking.  A  Bessemer  steel  has  been  made  better  by  merely 
submitting  it  to  the  heat  in  an  electric  furnace  for  a  short  time.  In  another 
case,  a  tool-steel  maker  found  that  he  could  produce  his  tool  steel  with 
smaller  additions  of  silicon  and  manganese  than  was  necessary  in  the 
crucible  process. 

The  only  explanation  that  appears  probable  is  that  the  higher  heat 
and  reducing,  rather  than  oxidizing,  atmosphere  of  the  electric  furnace, 
expels  some  of  the  gases  that  are  dissolved  in  the  steel,  and  possibly  aids 
the  removal  of  the  combined  oxygen,  thus  making  the  deoxidation  more 
complete  than  in  the  crucible. 

The  latest  development  in  the  electric  furnace  experiments  has  been 
the  combination  gas  and  electric  heated  furnace.  As  the  United  States 
Steel  Corporation  have  a  supply  of  natural  gas  at  their  plants  in  the  Pitts- 
burg  district,  they  have  built  a  tilting  open-hearth  furnace  in  which  a 
cold  charge  is  melted  down  with  gas,  after  which  it  is  turned  off  and  elec- 
trodes lowered  into  the  metal,  through  the  top  of  the  furnace,  to  refine 
the  charge. 

This  is  apparently  the  most  economical  method  of  making  electric 
steel  that  has  yet  been  suggested,  as  the  natural  gas  can  be  obtained  for 
less  than  20  cents  per  thousand  feet,  and  at  this  rate  is  much  cheaper 
than  electricity,  and  perhaps  just  as  good  for  melting  down  the  charge. 
The  use  of  the  electric  current  can  then  be  confined  to  removing  the 
impurities  from  the  bath.  This,  however,  is  in  the  experimental  stage 
and  what  the  cost  of  operation  will  be,  for  the  quality  of  steel  to  be  pro- 
duced, has  not  yet  been  established. 


CHAPTER  VI 
INGKEDIENTS  OF  AND  MATERIALS  USED  IN  STEEL 

THE  elements  entering  into  the  composition  of  steel  have  been  studied 
and  investigated  in  many  ways  and  their'  effects  have  been  carefully 
noted.  Many  new  alloying  materials  have  been  brought  into  use  in 
the  past  few  years.  These  were  made  available  by  the  high  temperature 
obtained  in  the  electric  furnace,  as  this  enables  them  to  be  separated 
from  the  elements  with  which  they  were  found,  and  combined  with  iron 
to  make  ferro-alloys  that  could  be  added  to  the  steel  in  its  making.  Many 
other  elements  are  being  experimented  with,  and  some  of  these  give  prom- 
ise of  adding  new  properties  to  steel  or  bettering  the  properties  already 
recognized  as  good  ones,  and  thus  we  may  be  able  in  the  near  future  to 
still  further  improve  it  in  quality. 

These  new  alloying  materials  have  given  us  steels  which,  for  strength, 
cutting  qualities,  wearing  qualities,  and  ability  to  withstand  vibrational 
and  torsional  stresses,  attain  a  higher  standard  of  excellence  than  would 
have  been  considered  possible  a  short  time  ago. 

CARBON   IN   STEEL 

Of  all  the  alloying  elements  entering  into  steel,  carbon  is  the  most 
important,  as  it  is  the  quantity  and  condition  of  the  carbon  in  the  metal 
that  makes  the  distinction  between  iron  and  steel.  The  distinctive  fea- 
tures of  different  grades  of  steel  are  due  more  to  the  variation  of  the  car- 
bon contents  than  to  the  differences  in  any  or  all  of  the  other  elements. 

One  of  the  wonders  of  metallurgy  is  the  effect  that  a  small  per  cent, 
of  carbon  has  upon  iron.  Pure  iron,  that  is,  iron  that  has  been  electro- 
lytically  deposited,  has  a  tensile  strength  of  45,000  pounds  per  square 
inch,  and  if  we  add  a  few  tenths  of  1%  of  carbon,  the  tensile  strength 
immediately  rises  to  60,000  pounds,  and  with  1%  it  reaches  120,000  pounds 
per  square  inch.  This  is  a  quantity  so  small  that  it  is  out  of  all  propor- 
tion to  the  mass  in  which  it  is  distributed. 

Carbon  unites  with  chemically  pure  iron  in  all  proportions  up  to  4J 
per  cent.  The  capacity  of  the  iron  for  carbon  can  be  increased  by  using 
manganese,  and  when  a  high  percentage  of  manganese  is  added  to  steel 
the  carbon  content  can  be  raised  to  7  or  8  per  cent.  Manganese,  sili- 
con, phosphorus,  sulphur,  etc.,  may  vary  widely  in  quantity,  but  the  carbon 

64 


INGREDIENTS  OF  AND   MATERIALS  USED  IN  STEEL  65 

usually  decides  the  class  in  which  the  steel  belongs;  for  the  carbon  gives 
greater  hardness  and  strength  to  the  steel,  with  less  brittfcness,  than  any 
other  element. 

To  get  the  desired  percentage  of  carbon  into  steel,  various  methods 
are  used.  In  the  melting  in  process,  that  is,  adding  the  carbon  to  the 
steel  when  the  metal  is  molten,  the  Bessemer,  open-hearth,  and  crucible 
processes  all  use  a  different  method.  Besides  this,  there  is  the  cementa- 
tion process  in  which  the  carbon  is  put  into  the  steel  while  in  a  solid  state. 
Several  methods  are  employed  in  this,  and  they  consist  of  submitting 
the  metal  to  the  action  of  some  carbonaceous  material  in  the  presence 
of  heat. 

In  the  Bessemer  process,  the  charge  of  molten  metal  is  put  into  the 
converter  and  air  is  blown  through  it.  This  air  oxidizes  out  all  of  the 
silicon  and  manganese  and  nearly  all  of  the  carbon,  the  heat  of  combus- 
tion of  these  elements  raising  the  temperature  of  the  charge.  The  charge 
is  then  recarburized  through  an  addition  of  molten  spiegeleisen,  after 
which  the  metal  is  poured  into  ingots. 

In  the  open-hearth  process,  the  charge  usually  consists  of  50%  pig 
iron  and  50%  of  scrap,  and  these  are  melted  up  together.  The  pig  iron 
usually  contains  from  3 J  to  4%.  of  carbon,  and  the  charge  is  melted  down 
and  boiled  until  the  carbon  has  been  reduced  by  oxidation  to  the  required 
amount.  Tests  are  taken  every  half  hour  or  so,  to  determine  when  the 
carbon  has  been  reduced  to  the  proper  percentage,  and  when  this  is  reached, 
the  ferro-alloys  are  added  to  the  bath  and  it  is  cast  into  ingots. 

In  the  crucible  process,  muck  iron  and  charcoal  is  charged,  the  crucible 
sealed  up  and  the  charge  melted  down.  If  the  muck  iron  contains  0.10% 
of  carbon,  100  pounds  of  muck  bar  and  15  ounces  of  charcoal,  which  is 
the  form  in  which  the  carbon  is  put  in  the  bath,  will  make  a  1%  carbon 
steel.  With  the  muck  iron  higher  or  lower  in  carbon,  the  charcoal  is 
diminished  or  increased  to  obtain  the  correct  carbon  content. 

By  the  cementation  process  muck  iron  is  changed  into  blister  bars, 
or  from  a  low  to  a  high  carbon  metal  by  placing  alternate  layers  of  iron 
and  charcoal  in  a  furnace  and  covering  the  top  with  clay  to  prevent  the 
charcoal  from  burning  off.  Much  iron  containing  about  0.10%  of  carbon 
is  usually  used.  By  closing  the  furnace,  heating  it  up  slowly  for  a  few 
days  and  then  keeping  it  at  a  good  yellow  heat  for  about  nine  days,  the 
iron  has  absorbed  about  1%  of  carbon.  This  product  is  often  used  for 
making  crucible  steel  by  merely  melting  it  down  in  the  pot  and  adding 
the  alloying  materials  that  are  desired  to  purify  and  strengthen  the  metal. 
This  process  is  also  used  in  Harveyizing  armorplate,  but  in  this  case  but 
two  plates  separated  by  one  layer  of  charcoal  are  used,  and  about  30  days' 
time  consumed;  ten  of  which  are  used  to  slowly  heat  the  metal  up  to  the 


66  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

desired  temperature,  at  which  it  is  retained  for  ten  more  days,  and  the 
final  ten  days  are  consumed  in  allowing  it  to  slowly  cool.  With  this 
treatment  the  carbon  has  penetrated  to  a  depth  of  from  1  to  li  inches 
and  the  surface  of  the  plate  will  show  about  2.50  per  cent,  of  carbon 
when  analyzed. 

The  Krupp  process  conducts  illuminating  gas  over  the  surface  of  the 
armorplate  instead  of  the  charcoal.  When  the  plate  is  at  a  good  yellow 
heat,  it  decomposes  this  gas  into  carbon  and  hjalrogen;  the  carbon  being 
deposited  on  the  plate  in  a  finely  divided  state  as  soot,  which  is  imme- 
diately absorbed  by  the  metal,  while  the  hydrogen  escapes  as  a  gas. 

Both  of  these  cementation  processes  are  used  with  various  modifica- 
tions for  carbonizing  small  pieces  in  special  furnaces,  and  this  subject 
is  treated  in  detail  under  the  chapter  on  Carbonizing.  A  low  carbon 
iron  or  steel  will  absorb  carbon  from  any  carbonaceous  material  in  the 
presence  of  heat;  in  fact,  if  two  pieces  of  metal  are  heated  to  the  proper 
temperature,  one  containing  a  high  and  the  other  a  low  percentage  of 
carbon,  the  carbon  will  flow  from  the  high  to  the  low  point.  Its  action 
under  these  conditions  is  very  similar  to  the  difference  in  potential  of 
an  electric  current,  which  always  flows  from  a  highly  charged  body  to 
that  of  a  lower,  until  an  equilibrium  has  been  established. 

The  actual  mode  of  existence  of  the  carbon  in  the  metal  is  of  great 
importance  in  the  working  and  treating  of  steel,  and  several  words  have 
been  coined  to  define  its  different  conditions.  Ferrite  means  carbonless 
iron,  and  its  chemical  abbreviation  is  Fe.  Cementite  consists  of  three 
atoms  of  iron  combined  with  one  atom  of  carbon,  FesC.  Graphite  is  the 
carbon  that  is  uncombined,  as,  when  an  excess  of  carbon  is  present  in 
iron,  all  that  will  combine  will  be  taken  up  by  the  iron  and  form  cement- 
ite,  while  the  balance  will  remain  in  a  free  state  or  as  graphitic  carbon. 
Pearlite  is  a  very  intimate  mechanical  mixture  of  ferrite  and  cementite, 
usually  in  alternate  layers,  and  Austenite  is  a  solid  solution  of  carbon  in 
iron.  Martensite,  Troostite,  Sorbite,  etc.,  are  transition  forms  that  are 
taken  up  under  the  chapter  entitled  "  Hardening  Steel." 

The  term  solid  solution  refers  to  that  association  of  substances  which 
is  neither  chemical  combination  nor  mechanical  mixture.  A  solid  solu- 
tion has  all  of  the  properties  of  a  liquid  solution,  such  as  salt  or  sugar 
when  dissolved  in  water,  except  liquidity.  It  is  distinguished  from  a 
chemical  compound  because  of  the  fact  that  the  constituents  may  vary 
in  the  proportions  in  which  they  are  present,  and  that  it  is  not  a  mechanical 
mixture  may  be  told  by  microscopic  observation.  Glass  is  a  familiar 
example  of  a  solid  solution. 

In  heating  and  cooling  steel,  the  carbon  assumes  different  forms,  as 
well  as  when  in  different  percentages.  In  heating  and  cooling  a  piece 


INGREDIENTS   OF   AND   MATERIALS   USED   IN    STEEL 


67 


of  annealed  steel  that  contains  about  30%  carbon  or  less,  it  goes  through 
the  changes  graphically  illustrated  in  Chart  1.  With  a  steel  containing 
not  more  than  0.90%  of  carbon,  it  is  almost  impossible  to  develop  any 
graphitic  carbon,  as  this  is  a  eutectoid  steel  that  contains  about  six  times  as 
much  pure  iron  by  weight  as  the  weight  of  the  cementite,  and  thus  it 
is  almost  impossible  to  force  the  carbon  into  the  graphitic  state.  The 
ability  to  produce  graphitic  carbon  is  greatly  decreased  as  the  carbon 
lowers  in  percentage. 

Starting  with  a  soft  or  annealed  bar  of  low-carbon  steel  at  atmospheric 
temperature,  which  has  been  designated  zero  on  the  chart,  the  temperature 
will  rise  uniformly  until  it  reaches  a  point  at  about  1300°  F.  Here  the  tern- 


Low 

(Tensile  Strength 
1KOF.AC8 


Highest 
Tensile 
HOO°F.  Ac  2 Strength    , 


Ar  3  1600  P. 


18CO  F. 


Acl  y— 'resC 


'Zero 


Ar2 18«f  E- 


Lowest  Tensile  Strength 

CHART  1. 


peraturc  hesitates  and  remains  stationary  until  certain  internal  condi- 
tions have  been  satisfied,  when  it  again  rises  uniformly  to  about  1400°  F., 
where  the  second  transformation  takes  place  in  the  metal,  and  the  tem- 
perature again  remains  stationary  until  this  has  been  completed,  and 
it  again  rises  uniformly  to  about  1550°  F.,  where  the  third  change  takes 
place.  These  have  been  designated  the  recalescent  points,  and  they 
have  been  named  Acl,  Ac2,  and  Ac3.  If  suddenly  cooled  at  the  upper 
point,  the  steel  will  be  made  very  hard,  and  the  metal  will  be  held  in 
the  condition  it  was  placed  by  the  applied  heat. 

If  allowed  to  cool  slowly  or  annealed,  the  temperature  will  drop  uni- 
formly until  slightly  below  the  temperature  at  which  the  transformation 
took  place  while  the  heat  was  rising,  or  about  1500°  F.,  and  the  metal 
will  then  slightly  rise  in  temperature.  This  point  has  been  designated 


68  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

Ar3.  When  the  alterations  in  the  structure  and  grain  have  been  com- 
pleted, the  temperature  again  falls  uniformly  until  it  reaches  a  tempera- 
ture of  about  1350°  F.,  at  which  point  the  second  change  takes  place,  that 
is  the  opposite  of  that  on  the  rising  temperature,  and  has  been  designated 
in  Ar2.  After  the  change  has  been  completed  at  this  point,  it  again  lowers 
in  temperature  uniformly  to  the  next  point,  or  Arl,  at  about  1250°  F., 
and  after  this  change  takes  place,  it  then  gradually  lowers  to  atmospheric 
temperature.  These  have  been  named  the  decalescent  points. 

While  opinions  differ  on  this  point,  what  probably  takes  place  is  that 
while  heating  the  steel  up  to  Acl  all  the  carbon  is  in  the  cementite  form, 
or  Fe3C.  When  this  point  is  reached,  the  heat  that  has  been  absorbed  by 
the  metal  causes  a  partial  decomposition  to  take  place  that  results  in  the 
dropping  of  one  atom  of  iron,  and  when  the  metal  has  completely  assumed 
the  form  of  Fe2C,  the  temperature  rises  to  Ac2,  where  it  drops  another  atom 
of  iron  and  the  carbon  assumes  the  form  of  FeC.  With  this  change  com- 
pleted, the  temperature  again  rises  to  Acl,  where  the  carbon  goes  into  solid 
solution  with  the  iron  or  the  Austenite  form. 

On  slowly  cooling  the  metal  from  this  point,  the  reverse  "action  takes 
place,  that  is,  at  Ar3  the  carbon  absorbs  one  atom  of  the  iron  that  has 
been  dropped  on  the  rising  temperature,  and  the  metal  becomes  FeC; 
while  at  the  next  point,  or  Ar2,  it  absorbs  the  second  atom  of  iron  that 
was  dropped  and  takes  the  form  of  Fe2C,  while  at  Arl  it  absorbs  the  third 
atom  of  iron  and  again  becomes  Fe3C,  or  cementite. 

During  these  changes  in  the  metal,  the  iron  assumes  three,  different 
conditions.  While  the  temperature  is  rising  up  to  Ac2  it  is  highly  mag- 
netic, and  is  called  alpha  (a)  iron.  At  Ac2  it  loses  its  magnetism  and 
between  Ac2  and  Ac3  it  is  as  non-magnetic  as  brass,  and  is  called  beta 
(j8)  iron.  This  change  in  magnetism  is  accompanied  by  a  change  in 
electric  conductivity  and  specific  heat.  At  Ac3  another  change  in  elec- 
trical conductivity  takes  place  and  also  in  the  crystalline  form.  Above 
Ac3  it  is  called  gamma  (y)  iron. 

The  carbon  content  of  steel  usually  varies  between  0.10  and  2%. 
Metal  having  more  than  2%  is  called  cast  iron  and  used  as  such.  Until 
recently  wrought  iron  was  about  the  only  useful  iron  product  that  contains 
less  than  0.10%  of  carbon,  but  this  is  made  by  a  working  instead  of  a 
casting  process.  Now,  however,  so-called  " ingot  iron,"  consisting  of 
about  99.9%  of  pure  iron,  with  only  a  trace  of  carbon,  is  made  commercially. 

With  a  carbon  content  of  from  0.10  to  0.30%,  steel  is  soft  and  cannot 
be  hardened  enough  to  prevent  cutting  with  a  file.  It  is  then  called 
machinery,  soft,  or  low  carbon  steel.  With  a  carbon  content  of  from 
0.30  to  2%  it  can  be  hardened  so  as  to  cut  other  steels  or  metals,  and  is 
then  called  tool,  half  hard,  hard  or  high-carbon  steel,  according  to  the 
carbon  content.  Exceptions  to  the  above  statement  may  be  made  in  hard 


INGREDIENTS   OF   AND    MATERIALS   USED   IN    STEEL 


69 


steels,   as  a  low-carbon  steel  can  be  made*  hard  by  either  manganese, 
tungsten,  or  chromium,  but  it  is  true  of  soft  steel. 

Every  increase  in  the  percentage  of  carbon  increases  the  hardness 
and  brittleness,  and  therefore  its  liability  to  fracture  when  cold  or  when 
heated  suddenly,  while  it  reduces  the  elongation  and  reduction  of  area. 
The  tenacity  shows  a  relatively  quick  rise  up  to  0.90%  of  carbon,  and  a 
slow  rise  from  there  to  1.20%  carbon,  after  which  it  decreases.  The  rela- 
tive ductility  decreases  in  an  irregular  curve  with  an  increasing  carbon 
content.  These  properties  are  graphically  shown  in  the  chart  (Fig.  43), 
while  the  separation  of  the  ferrite  and  carbon  and  the  formation  of 
graphitic  carbon  are  shown  by  Fig.  44. 


Percentage  of  Carbon 

8  8  8  %  8  8  S  8  8  $  3  $  8  9  3  8  £  8  8  3 

O      doOOO      OO      O     vH     <-i     iH      M«Mv4*4v4v4v4OT 


20,000 


jtofFe3C     0  5  10  15  20  25  30 

*  of  Ferrite  100  95  90  85  80  75  70 

FIG.  43.  —  Effect  of  carbon  on  physical  properties  of  steel. 


The  strength  of  steel  is  always  secured  at  the  sacrifice  of  some  other 
desirable  property,  but  the  sacrifice  is  less  in  the  case  of  carbon  than  with 
any  other  element.  The  tensile  strength  and  elastic  limit  are  raised  con- 
siderably by  hardening,  and  the  higher  the  percentage  of  carbon  the  greater 
the  degree  of  hardness  that  can  be  attained.  But  the  greater  the  carbon 
content  the  less  will  be  the  elongation,  as  hardened  high  carbon  steel 
is  very  brittle.  This  brittleness  makes  high  carbon  steel  very  easily 
damaged  in  heat  treating  or  working,  and  the  carbon  content  is  usually 
kept  as  low  as  possible  for  the  strength  and  hardness  that  is  desired. 
"  Sudden  rupture"  is  a  term  which  is  especially  applicable  as  a  character- 
istic of  carbon  steel  products,  and  a  large  amount  of  effort  is  being  expended 
to  discover  either  new  ingredients,  new  methods  of  manufacture,  or  new 
ways  of  treating  the  metal  that  will  overcome  this  characteristic. 


70 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


Some  investigations  that  have  been  carried  on  prove  that  beginning 
with  pure  steel,  which  has  a  tensile  strength  of  40,000  pounds  per  square 
inch,  every  increase  of  0.01%  of  carbon,  up  to  about  1%,  increase  the 
strength  of  acid  open  hard  steel  about  1000  pounds,  and  basic  open 
hard  steel  770  pounds  per  square  inch.  As  the  color  method  of  deter- 
mining the  carbon  content  does  not  show  all  the  carbon  present,  these 
figures,  however,  should  be  changed  to  1140  and  820  pounds  respectively, 
when  the  color  method  of  analysis  is  used. 


27CC 
2000 

^ 

\ 

X 

x 

\ 

\ 

x 

v 

\ 

\. 

<£ 

\ 

\ 

\ 

^ 

,S 

\ 

Uau 
+  Sol 

id  Bolu  lonX 
d  Solution 

Liquid  fcoluttoi 
\                             > 

/' 

Ll^u 

dSolut 

on 

2100 
2000 
1800 
1800 
1700 

1600 
ft 

160C 
1400 

1300 
1200 
1100 
1000 
900 

Solid 

«* 

Iron^, 

\ 

\ 

\y 

+ 

Jraphit 

^ 

G»m. 

a  Solid 

Solutio 

n-1-Gr.j 

bit« 

<Hmt 

a  Iron 

Fe6C 

Fi 

6C+G 

•»pblt« 

> 

V 

5X 

ol  n.)^ 

| 

V    / 

6 

mm»J 

on±Fe 

tc 

a  iron 

I  SoM 

so 

. 

Jphalr 

utF., 

P 

Alpha  I 

ron-t-Fe 

2° 

123 

Percent  Carbon 

FIG.  44.  —  Effect  of  temperature  on  carbon. 

Probably  Bessemer  steel  would  show  lower  figures  than  this  and 
crucible  or  electric  steel  higher  figures.  This  is  doubtless  due  to  the  fact 
that  some  processes  of  steel  making  remove  the  oxides  and  occluded 
gases  better,  or  to  a  greater  extent,  than  others,  and  it  has  been  pretty 
well  demonstrated  that  these  are  injurious  to  the  strength  and  life  of  steel. 


INGREDIENTS   OF   AND   MATERIALS   USED   IN   STEEL  71 

alter  these  figures,  but  with  all  other  conditions  equal  they  will  probably 
hold  good. 

That  the  maximum  strength  is  placed  at  about  1%  carbon  is  probably 
due,  to  a  great  extent,  to  the  fact  that  the  crystalline  constituents  form 
an  intimate  mixture  near  the  eutectoid  proportions,  and  hence  the  crys- 
tallization is  very  small  comparatively.  With  more  carbon  (cementite) 
present  the  pearlite  grains  are  surrounded  with  a  network  of  cementite, 
while  with  less  the  pearlite  grains  are  surrounded  with  a  network  of 
ferrite,  and  both  of  these  decrease  the  cohesive  force  inherent  in  the  metal. 

One  of  the  oldest  theories  as  to  what  made  high-carbon  or  tool  steel 
harden  was  that  the  carbon  in  unhardened  steel  was  partially  in  the 
graphitic  and  uncombined  form,  and  when  it  was  hardened  all  the  carbon 
assumed  the  combined  form.  The  most  generally  accepted  theory,  how- 
ever, assumes  that  the  hardness  is  due  partly  to  the  presence  of  the  solid 
solution  of  carbon  in  iron,  and  partly  to  the  iron  being  in  the  gamma  or 
beta  forms.  This  solid  solution  of  carbon  in  gamma  or  beta  iron  is  exceed- 
ingly hard  and  it  is  preserved  in  the  steel  by  quenching  from  above  the 
critical  temperature. 

MANGANESE 

Manganese  occurs  in  nature  principally  in  the  form  of  manganese 
dioxide  (Mn02),  which  is  commonly  called  black  oxide  of  manganese, 
but  occasionally  it  is  found  in  other  compounds,  such  as  braunite,  man- 
ganite,  carbonate,  etc.  Some  of  its  compounds  with  oxygen  and  hydrogen 
are  distinctly  acids  while  others  are  distinctly  basic,  and  it  is  in  connec- 
tion with  the  base-forming  elements  that  it  is  of  interest  in  steel  making. 
For  use  in  steel  making  the  dioxide  is  separated  from  its  oxygen,  in  the 
presence  of  charcoal  or  coke,  either  in  the  blast  furnace  or  in  an  electric  fur- 
nace. It  looks  like  cast  iron,  is  brittle  and  hard,  and  is  combined  with 
iron  to  form  ferro-manganese.  Sometimes  silicon  is  added  to  form  ferro- 
silicon-manganese. 

Manganese  is  an  element  that  is  always  found  in  steel,  but  its  true 
properties  and  effects  were  not  known  until  about  twenty  years  ago, 
when  they  were  discovered  by  R.  A.  Hadfield,  a  metallurgist  and  steel 
maker  of  Sheffield,  England.  Its  effect  when  added  to  steel  up  to  2% 
with  various  percentages  of  carbon  is  best  shown  by  Fig.  45,  the  actual 
mode  of  existence  of  the  carbon  in  the  steel  being  very  important. 

When  more  than  2%  and  less  than  6%  of  manganese  is  added,  with 
the  carbon  less  than  0.5%,  it  makes  steel  very  brittle,  so  that  it  can  be 
powdered  under  a  hand  hammer.  From  6%  of  manganese  up,  this  brittle- 
ness  gradually  disappears  until  12%  is  reached,  when  the  former  strength 
returns  and  reaches  its  maximum  at  about  14%.  After  this  a  decrease 
in  toughness,  but  not  in  transverse  strength,  takes  place,  until  20%  is 


72 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


reached,   after  which  a  rapid  decrease  again  takes  place.     Manganese 
may  affect  the  tensile  strength  and  ductility  of  steel,  either  indirectly 


.4        £       .6       .7       A        .9      1.0 

Percentage  of  Cartxw 


FIG.    45.  —  Effect    of    manganese    below 

2    per    cent.  , 

by  retarding  the  formation  of  blow-holes,   or  directly  by  entering  into 
chemical  combination  with  the  metal. 


10      11      12     13      14      15     16      17      18     19      20 

Percentage  of  Manganese 

FIG.  46.  —  Effect  of  Manganese  above  6  per  cent. 

Fig.  46  shows  the   effect  of  more  than  6%   of  manganese  on  the 
tensile  strength  and  elongation. 


INGREDIENTS  OF  AND  MATERIALS  USED  IN  STEEL  73 

Steel  with  from  10  to  15%  of  manganese  and  less  than  0.50%  of  car- 
bon is  very  hard  and  cannot  be  machined  or  drilled  in  the  ordinary  way; 
yet  it  is  so  tough  that  it  can  be  twisted  and  bent  into  peculiar  shapes 
without  breaking.  This  makes  a  steel  that  is  only  suitable  for  casting 
into  the  desired  shape.  A  process  has  recently  been  patented  however, 
for  casting  this  steel  into  ingots,  and  then  subjecting  them  to  a  heat  treat- 
ment that  enables  them  to  be  mechanically  worked;  that  is  rolled,  forged, 
etc.,  and  this  might  possibly  be  extended  to  machining  operation. 

Manganese  in  the  form  of  a  ferro-alloy  containing  about  80%  of  man- 
ganese is  added  to  a  heat  of  steel  at  the  time  of  tapping,  so  that  it  may 
seize  the  oxygen  which  is  dissolved  in  the  bath  and  transfer  it  to  the  slag 
as  oxide  of  manganese.  Manganese  prevents  the  coarse  crystallization 
that  the  impurities  would  otherwise  induce,  and  steels  low  in  phosphorus 
and  sulphur  require  less  manganese  than  those  having  comparatively  high 
and  percentages. 

Manganese  has  a  greater  affinity  than  iron  for  both  sulphur  and  oxygen, 
and  is  therefore  used  in  steel  making  as  a  deoxidizer  and  to  neutralize  the 
sulphur.  Manganese  oxide  (MnO)  and  manganese  sulphide  (MnS)  are 
formed,  the  first  of  which  passes  almost  entirely  into  the  slag  and  the  sec- 
ond of  which  will  pass  partly  into  the  slag  if  time  is  allowed.  About  four 
times  as  much  manganese  is  needed  as  there  is  sulphur  present,  as  it  does 
not  always  catch  all  of  the  sulphur;  thus  if  any  great  amount  of  sulphur 
is  present  a  considerable  amount  of  manganese  is  desired  to  counteract 
its  effect.  If  the  bath  is  kept  liquid  enough  and  enough  manganese  is 
present,  but  little  oxygen  or  sulphur  will  be  found  combined  with  the  iron, 
which  is  desirable  as  they  are  very  injurious  to  the  metal.  The  length  of 
time  and  the  care  required,  however,  make  it  commercially  impractical  to 
reduce  the  oxygen  and  sulphur  to  a  trace  in  this  way.  Therefore  man- 
ganese is  used  to  reduce  them  to  commercial  percentages,  and  other  mate- 
rials are  used  to  still  further  remove  them  for  the  finer  grades  of  steel. 
Manganese  sulphide  weakens  steel  greatly  if  segregated  together  with 
phosphide  of  iron,  especially  if  the  metal  is  rolled,  as  this  magnifies  the 
sulphide  by  spreading  it  out  during  rolling. 

Manganese  is  not  only  useful  to  cleanse  the  bath  of  impurities,  but 
it  has  other  properties  that  aid  in  making  steel  better.  The  amount 
that  can  be  left  in  the  steel  varies  with  the  amount  of  various  other  ingre- 
dients that  are  added  to  the  metal,  and  this  is  especially  so  of  carbon. 
In  effect  it  behaves  in  practically  the  same  manner  as  carbon,  as  also 
does  nickel.  With  a  given  carbon  content  the  introduction  and  increase 
of  manganese  causes  a  series  of  structural  changes  similar  to  those 
that  occur  in  carbon  steels,  that  only  contain  small  percentages  of 
manganese. 

While  the  action  of  these  three  elements  upon  iron  is  of  the  same  kind, 


74  COMPOSITION  AND  HEAT-TREATMENT  OF   STEEL 

it  is  not  of  the  same  strength,  as  the  equivalent  of  1%  of  total  carbon, 
that  contains  the  maximum  amount  of  hardening  carbon,  is  7.25%  of 
manganese  and  17.55%  of  nickel.  All  three  of  these  cause  a  structural 
change  in  the  metal  from  pearlite,  that  includes  the  sorbitic,  to  marten- 
site,  that  includes  the  troostitic,  and  then  to  the  polyhedral  structure, 
and  with  none  of  them  is  a  special  carbide  formed.  Chromium  has  an 
analogous  effect,  but  not  as  complete,  as  a  double  carbide  of  iron  and 
chromium  forms  and  this  is  not  maintained  in  solution  in  the  iron  without 
tempering. 

The  critical  temperature  to  which  it  is  safe  to  heat  steel  is  raised  by 
manganese,  owing  to  its  resisting  the  separation  of  the  crystals  in  cooling 
from  liquid,  and  conferring  the  quality  of  hot  ductility.  It  also  assists" 
in  producing  more  uniform  alloys,  and  tends  to  make  steel  crystals  smaller 
by  making  the  metal  plastic,  and  thus  counteracting  the  tendency  toward 
crystallization  that  phosphorus  causes,  although  the  metal  is  more  liable 
to  crack  when  heating  or  suddenly  cooling  it  from  a  red  heat.  The  good 
qualities  more  than  offset  the  bad,  and  it  is  a  very  useful  factor  in  steel 
making  if  the  proper  percentages  are  used.  It  atones  for  many  evils 
in  steel  by  healing  it  up  and  producing  a  smoothly  rolled  surface. 

In  the  ordinary  steels  this  percentage  is  usually  from  0.70  to  1.00%, 
while  in  many  of  the  special  alloys  it  runs  from  0.30  to  0.50%.  In  the 
high-speed  steels  the  manganese  content  is  from  0.10  to  0.30%,  and  in 
steels  for  carbonizing  this  should  be  kept  below  0.20%.  When  in  very 
large  amounts  (from  6.0  to  15.0%)  it  reverses  the  effects  of  rate  of  cool- 
ing upon  the  ductility  of  steel;  slow  cooling  making  manganese  steel 
brittle,  while  quick  cooling  makes  it  extremely  ductile. 

Magnetic  qualities  are  not  materially  effected  when  the  manganese  is 
kept  below  7.50%.  When  8%,  or  more,  is  present,  however,  the  mag- 
netic attraction  becomes  nil.  Manganese  decreases  the  electric  con- 
ductivity in  greater  proportions  than  any  other  element,  except  nickel. 
Thus  third  rails,  or  similar  steels,  must  be  given  their  hardness  by 
materials  other  than  nickel  or  manganese.  A  peculiar  fact  that  was 
brought  out  by  some  experiments  was  that  a  pure  nickel-iron  alloy  that 
contained  from  12  to  13%  of  nickel  was  highly  magnetic,  but  by  the 
addition  of  5%  of  manganese  this  metal  became  as  non-magnetic  as 
brass.  While  manganese  steels  are  known  to  be  non-magnetic,  it  was 
not  known  that  manganese  would  have  this  effect  upon  nickel,  which 
also  makes  a  non-magnetic  steel  when  added  in  certain  proportion. 

To  sum  up,  manganese  alloys  with  iron  in  all  ratios,  it  being  reduced 
from  its  oxides  at  a  white  heat  by  carbon.  Its  presence  increases  the 
power  of  carbon  to  combine  with  iron  at  a  very  high  temperature 
(about  2550°  F.),  and  almost  entirely  prevents  its  separation  into 
graphitic,  carbon  at  the  lower  temperatures,  Manganese  permits  a 


INGREDIENTS   OF   AND   MATERIALS   USED   IN   STEEL  75 

higher  total  carbon  by  raising  the  saturation  point,  and  it  is  easily 
separated  from  iron  by  oxidation,  as  it  is  even  oxidized  by  silica. 
While  it  does  not  counteract  the  cold  shortness  caused  by  phosphorus, 
it  does  prevent  to  some  extent  the  red  and  yellow  hot  shortness  caused 
by  sulphur. 

Manganese  retards  the  formation  of  blow-holes,  though  not  to  the 
extent  that  silicon  does,  by  preventing  the  oxidation  of  carbon,  and  thus 
the  formation  of  carbonic  oxide.  It  also  increases  the  solubility  of  the 
gases  in  the  steel  while  solidifying.  It  probably  raises  the  elastic  limit 
and  slightly  increases  the  tensile  strength;  adds  fluidity  to  the  metal; 
increases  hardness;  increases  fusibility  when  present  in  considerable  quan- 
tity, and  gives  greater  plasticity  and  mobility  to  the  metal  at  forging  heats. 
Some  recent  investigations,  however,  make  it  doubtful  that  it  diminishes 
ductility  to  any  extent. 

SILICON 

Silicon  is  the  second  most  important  element  in  the  solid  part  of  the 
earth's  crust,  oxygen  being  first,  and  forms  27.21%  of  it.  It  is  never  found 
in  the  free  state  of  nature,  but,  having  a  powerful  affinity  for  oxygen,  it 
occurs  chiefly  as  silicon  dioxide  (Si02),  which  is  commonly  called  silica, 
and  in  the  form  of  silicates  in  combination  with  oxygen  and  such  metallic 
elements  as  sodium,  potassium,  aluminum,  and  calcium.  Silica  will 
neutralize  any  base  with  which  it  comes  in  contact  when  molten,  and  all 
metallurgical  slags  are  silicates  thus  formed.  The  silicon  used  in  steel 
making  has  to  be  separated  from  the  oxygen  of  the  silica  and  united  with 
iron  to  make  ferro-silicon.  Sometimes  manganese  is  added  to  this  to 
form  ferro-silicon-manganese. 

Many  contradictory  statements  have  been  made  as  to  the  effect  of 
silicon  on  steel.  When  the  silicon  is  high  in  Bessemer  steelyt  is  an  indica- 
tion that  the  metal  has  been  blown  too  hot,  and  the  metal  is  apt  to  be 
brittle.  The  percentage  varies  considerably,  according  to  the  heat  of 
the  charge,  and  this  causes  irregularities  which  may  account  for  the  differ- 
ence of  opinion.  The  melting  point  and  specific  weight  of  pig  iron  are 
governed  chiefly  by  the  silicon  and  the  carbon,  which  are  the  principal 
elements.  To  obtain  strength  and  density  the  silicon  and  carbon  should 
both  be  low.  The  hardness  should  be  controlled  by  a  careful  adjustment 
of  the  sulphur,  manganese,  and  phosphorus,  together  with  a  study  of 
their  effect  on  the  final  condition  of  the  carbon.  In  making  castings 
high  and  low  silicon  irons  should  never  be  mixed.  To  get  the  best 
results  in  the  steel  the  silicon  should  be  eliminated  as  much  as  pos- 
sible from  the  iron  and  a  definite  quantity  added  in  the  form  of  high 
percentage  ferro-silicon,  or  ferro-manganese-silicon.  This  gives  a  very 
different  effect  from  that  of  silicon  left  in  the  process  of  manufacture. 


76  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

If  silicon  is  added  to  steel  in  such  a  manner  as  to  cause  it  to  enter 
into  solution  as  silicide,  it  confers  upon  the  metal  valuable  properties; 
but  if  it  forms  a  silicate  it  is  injurious  in  many  ways,  even  to  the  point 
of  being  dangerous.  This  latter  seldom  occurs,  or  at  least  occurs  only 
to  a  slight 'degree,  as  the  silicates  of  iron,  manganese,  etc.,  dissolve  into 
each  other  very  readily  and  form  a  slag;  although  manganese  silicate 
probably  occurs  more  frequently  and  causes  more  failures  in  steel  than 
is  generally  supposed. 

Silicon,  having  a  great  affinity  for  oxygen,  it  seizes  this  wherever  found, 
and  carries  it  off  into  the  slag,  whether  in  the  form  of  gases,  oxides,  or 
dissolved  oxygen.  This  prevents  the  formation  of  blow-holes,  and  makes 
the  steel  harder  and  tougher.  Thus  it  is  better  able  to  withstand  wear 
or  crushing  from  continual  pounding.  This  is  only  so,  however,  when 
the  silicon  has  been  eliminated  as  far  as  possible  from  the  pig  iron  and  is 
again  added  to  the  steel  bath  in  the  form  of  ferro-silicon  or  silicon  spiegel. 
Otherwise  the  steel  is  liable  to  show  brittleness  and  irregularity  of  per- 
centage. 

One  steel  maker  found  that  if  the  percentage  of  manganese  plus  5.2 
times  the  percentage  of  silicon  were  made  to  equal  2.05,  the  metal  would 
be  entirely  free  from  blow-holes,  but  the  pipe  would  be  large;  if  the  total 
was  made  to  equal  1.66%,  the  pipe  would  be  smaller  and  numerous 
minute  blow-holes  would  appear,  but  not  enough  to  harm  the  steel  for  the 
use  to  which  it  was  to  be  put.  He  also  found  that  0.0184%  of  aluminum 
would  give  the  same  result  as  the  1.66%  of  manganese  and  silicon. 

In  the  Bessemer  converters  the  silicon  increases  the  temperature  of 
the  bath.  Thus  the  lower  the  percentage  of  the  silicon  in  the  pig  iron  the 
shorter  will  be  the  blow.  At  the  end  of  the  blow,  0.2%  of  silicon  is  added 
to  rid  the  bath  of  the  gases.  Thus  the  percentage  of  silicon  is  usually 
under  0.2  in  Bessemer  steel,  and  for  steel  rails  many  engineers  are  limiting 
it  to  0.1%. 

During  the  " killing"  in  the  crucible  process  the  steel  absorbs  silicon 
from  the  crucible  and  thus  becomes  sound  by  throwing  off  the  gases. 
The  graphite  crucibles  used  in  this  country  give  up  more  silicon  than  the 
clay  crucibles  used  in  Europe,  and  consequently  allowances  have  to  be 
made  when  charging.  Too  long  " killing"  makes  the  steel  harsh,  brittle, 
and  weak,  owing  to  its  absorbing  too  much  silicon.  Crucible  steels  nearly 
always  contain  more  than  0.2%}  of  silicon. 

The  influence  of  silicon  on  the  results  of  quenching  is  similar  to  that 
of  carbon  in  many  ways.  It  is  also  dependent  upon  the  coexisting  amount 
of  carbon  and  manganese.  It  neutralizes  the  injurious  tendency  of  man- 
ganese to  some  extent. 

An  increase  in  the  percentage  of  silicon  slightly  raises  the  tensile 
strength  and  lowers  the  elongation  and  reduction  of  area.  Up  to  a 


INGREDIENTS   OF   AND   MATERIALS   USED   IN   STEEL  77 

content  of  4%,  silicon  increases  the  tensile  strength  about  80  pounds  per 
square  inch  for  every  0.01%.  Beyond  this  amount  a  weakening  of  the 
metal  seems  to  ta*ke  place.  Without  a  considerable  percentage  of 
manganese,  silicon  steels  show  very  low  shock  resistance,  whether 
annealed  or  quenched.  With  0.20%  of  silicon  the  tensile  strength  is 
increased  about  one-third  more  than  0.01%  of  carbon  would  increase  it. 
Beyond  a  content  of  5.0%  silicon  steels  are  but  little  used  for  any 
purposes. 

Steels  containing  a  little  less  than  1%  of  carbon  and  from  1  to  2% 
of  silicon  have  been  used  quite  successfully  for  hard-tool  steels.  Below 
a  content  of  1%  silicon  ceases  to  have  an  influence  on  quenching  and  the 
metal  may  be  classed  as  a  special  carbon  steel.  Some  makers  of  steel 
try  to  keep  the  silicon  as  low  as  possible,  but  many  of  the  best  steels  con- 
tain from  0.20  to  0.80%.  With  the  carbon  content  low  the  silicon  may 
be  raised  to  a  fairly  high  figure,  but  with  the  carbon  high  the  silicon  should 
be  kept  low.  It  should  also  be  kept  low  when  the  phosphorus  is  high. 

Silicon  steels  are  extremely  fibrous  with  a  remarkable  resistance  to 
shock  in  the  direction  of  lamination,  but  practically  no  resistance  in  a 
direction  perpendicular  thereto.  This  quality  makes  them  especially 
adapted  for  leaf  springs. 

Ferro-silicon,  as  now  made  in  the  electric  furnace,  with  a  silicon  con- 
tent between  30  and  60%,  is  very  brittle  and  liable %to  disintegrate  spon- 
taneously, even  though  made  of  comparatively  pure  material.  With 
the  silicon  in  any  percentage  from  30  to  40  and  47  to  65,  it  gives  off  quite 
large  quantities  of  hydrogen  phosphide  gas,  especially  when  attacked  by 
moisture  in  any  form.  This  is  generated  from  calcium  phosphide,  which 
in  turn  is  formed  from  the  calcium  phosphate,  that  is  present  in  the  quartz 
and  anthracite,  when  it  is  submitted  to  the  high  temperature  of  the  elec- 
tric furnace.  Smaller  amounts  of  hydrogen  arsenide  are  also  evolved, 
and  both  of  these  are  highly  poisonous.  When  the  ferro-silicon  disinte- 
grates, the  amount  evolved  is  greater,  owing  to  the  largely  increased 
surface  that  is  exposed. 

Several  fatal  accidents  by  explosions  and  poisoning  have  been  caused 
from  these  gases  since  ferro-silicon  has  been  manufactured  in  the  elec- 
tric furnace.  Most  of  these  have  occurred  when  shipping  it  on  boats, 
as  there  is  then  more  moisture  to  attack  it.  When  the  silicon  content  is 
below  30  or  above  65%  these  gases  do  not  appear  to  evolve  in  amounts 
that  are  dangerous.  As  it  is  not  really  necessary  to  use  the  alloys  between 
these  percentages  for  the  manufacture  of  any  of  the  iron  products,  unless 
it  be  for  basic  furnace  steel,  their  use,  if  not  their  manufacture,  should  be 
prohibited.  Where  absolutely  necessary  to  use  them,  the  ferro-silicon 
should  be  broken  up  into  usable  sizes  and  completely  exposed  to  the  air 
for  at  least  one  month  before  shipping.  It  should  then  be  stored  in  a 


78  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

place  where  there  is  plenty  of  ventilation  to  carry  off  the  gases.  Ferro- 
silicon  made  in  a  blast  furnace,  however,  does  not  give  off  any  of  these 
gases,  and  there  is  a  movement  started  in  Europe  by  the  electric  furnace 
ferro-silicon  makers  to  abandon  the  manufacture  of  this  alloy  in  the 
dangerous  percentages. 

PHOSPHORUS 

Phosphorus  always  occurs  in  nature  in  the  combined  condition,  in 
the  form  of  phosphates,  derived  from  orthophosphoric  acid  H3PO4,  or  in 
the  form  of  organic  compounds.  It  unites  with  metals  to  form  phos- 
phides. It  forms  two  oxides,  namely,  P2O3  and  P2O5,  and  also  forms 
compounds  of  the  same  character  and  analogous  composition  to  arsenic, 
antimony,  and  bismuth.  It  is  consequently  placed  in  the  same  chemical 
group  as  these. 

It  is  always  encountered  in  reducing  iron  ores,  and  is  a  very  difficult 
element  to  remove  entirely  from  the  finished  iron  and  steel  product.  In 
these  materials  it  must  be  reduced  to  as  low  a  percentage  as  possible, 
as  phosphorus  is  without  doubt  the  most  injurious  element  that  is  found 
in  steel,  notwithstanding  the  fact  that  in  the  past  many  experiments  have 
been  carried  on  that  apparently  proved  that  phosphorus,  up  to  about 
0.12%,  strengthened  steel.  When  these  same  steels  were  put  into  actual 
use,  however,  failures  occurred,  and  the  cause  was  nearly  always  traceable 
to  the  phosphorus. 

In  the  rolling  mills  phosphorus  does  not  show  any  bad  effect,  as  the 
heat  under  which  the  steel  is  worked  seems  to  overcome  this,  but  when 
the  metal  has  become  cooled  and  is  subjected  to  sudden  shock  or  to  vibra- 
tional  stresses,  it  breaks  very  easily.  The  lower  the  temperature  and  the 
higher  the  atmosphere  the  easier  will  the  breaks  occur.  This  has  led  to 
the  term,  "  cold-shortness,"  as  applied  to  the  effect  of  phosphorus  on 
steel. 

Phosphorus  diminishes  the  ductility  of  steel  under  gradually  applied 
load,  as  shown  by  the  reduction  of  area,  elongation,  and  elastic  ratio  when 
specimens  are  pulled  apart  in  the  ordinary  static  strength  testing  machines. 
But  when  the  steel  is  tested  in  rotary  or  alternating  vibration  testing 
machines,  as  well  as  with  a  pendulum  impact  machine,  the  decrease  in 
ductility  and  toughness  is  shown  to  a  greater  degree.  Phosphorus  also 
reduces  deflection,  and  the  rigidity  thus  imparted  might  be  considered 
an  advantage  for  structural  purposes  except  for  the  metal's  weakness  at 
low  temperatures  and  when  subjected  to  shocks. 

Phosphorus  steels  are  so  capricious  that  they  may  show  a  reasonably 
high  static  ductility  and  still  show  very  brittle  when  shock  tests  are  applied. 
Therefore  the  safest  rule  to  apply  is  to  have  the  phosphorus  in  all  steel 
products  as  low  as  possible.  It  is  a  very  poor  steel  that  contains  0.10% 


INGREDIENTS   OF   AND   MATERIALS   USED   IN   STEEL  79 

of  phosphorus.  The  ordinary  grades  contain  as  much  as  0.08%,  and  the 
high-grade  steels  should  have  less  than  0.04%,  while  in  the  very  best 
steels  it  should  be  even  lower  than  this.  In  fact,  this  has  been  reduced 
to  below  0.01%  in  some  of  the  electric  furnace  steels,  and  occasionally 
a  mere  trace  is  all  that  is  left  in  the  finished  product. 

Phosphorus  gets  into  the  metal  by  entering  the  blast  furnace  with 
the  ores  in  the  form  of  metallic  phosphates,  —  the  form  in  which  it  is 
usually  found  in  nature,  —  and  mainly  as  phosphate  of  lime,  which 
occurs  as  a  natural  mineral  named  apatite.  Many  metallic  oxides 
unite  with  it  to  form  salts,  especially  iron  and  magnesium  oxides  and 
lime,  but  in  the  presence  of  silica,  which  is  a  stronger  acid,  it  is  driven 
out  of  the  slags  and  returned  to  the  iron  until  the  silica  has  been  satisfied 
with  bases. 

In  steel,  phosphorus  has  a  tendency  to  cause  coarse  crystals  to  form, 
and  this  tendency  is  increased  with  each  percentage  of  carbon.  It  forms 
the  phosphide,  Fe3P,  and  this  forms  a  series  of  alloys  with  iron.  The 
eutectic  of  this  series  contains  64%  of  this  phosphide,  which  equals  10.24% 
of  phosphorus.  A  certain  percentage  of  phosphorus  will  dissolve  in  pure 
iron  and  no  eutectic  will  form  to  produce  brittleness,  but  when  carbon  is 
added,  each  increase  in  percentage  exerts  an  influence  on  the  phosphorus 
that  causes  it  to  precipitate  from  the  solid  ferrite  solution  and  take  the 
eutectic  form.  Therefore  the  more  pure  the  iron  and  the  less  cementite 
that  is  in  the  steel,  the  less  will  be  the  brittleness  that  is  caused  by  phos- 
phorus, while  each  increase  in  the  percentage  of  carbon -increases  the 
tendency  of  the  eutectic  to  form  and  the  steel  to  assume  a  coarser  crystal- 
lization, which  makes  it  both  weaker  and  more  brittle. 

Phosphorus  is  removed  from  steel  to  a  different  degree  by  the  different 
processes  of  manufacture.  Thus  Bessemer  steel  usually  contains  the 
highest  percentage  of  phosphorus,  while  the  other  steels  contain  gradually 
decreasing  percentages  in  the  order  in  which  they  are  named:  acid  open- 
hearth;  basic  open-hearth;  crucible;  electric.  The  acid  open-hearth  fur- 
nace requires  materials  low  in  phosphorus,  while  in  the  basic  it  is  removed 
by  adding  a  sufficient  amount  of  lime  to  the  slag,  and  in  electric  furnaces 
it  is  removed  by  using  the  proper  flux. 

One  of  the  latest  methods  consists  of  using  an  oxidizing  slag  in  such 
a  way  that  it  will  combine  with  the  phosphorus  and  form  a  phosphate, 
and  then  adding  a  reducing  material  to  the  slag  that  will  convert  this 
phosphate  into  a  phosphide.  The  reducing  material  is  usually  ground 
coke  that  floats  on  top  of  the  slag  and  reduces  the  phosphate  without 
interfering  with  the  molten  metal  below.  Owing  to  the  strong  com- 
bination of  the  phosphide,  the  phosphorus  cannot  be  separated  out  by 
the  iron,  without  first  being  changed  back  to  phosphate,  and  this  is  impos- 
sible in  a  reducing  atmosphere. 


80  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

One  charge  that  was  dephosphorized  in  the  Heroult  electric  furnace, 
when  taken  from  a  Bessemer  converter,  analyzed:  phosphorus,  0.10%, 
sulphur,  0.16%,  manganese,  0.10%,  carbon,  0.07%,  and  silicon,  traces. 
A  15-ton  charge  of  this  was  put  in  the  Heroult  furnace  and  a  black  slag 
composed  of  400  pounds  each  of  mill  scale  and  lime  was  added.  This  made 
an  oxidizing  slag  that  became  fluid  when  the  molten  metal  below  was 
thoroughly  oxidized,  and  all  the  phosphorus  passed  into  the  slag  as 
phosphate  of  lime  (CaO).  Ground  coke  was  then  added  to  the  top  of 
the  slag,  and  this  reduced  the  phosphates  there  into  calcium  phosphide 
(P2Ca3).  Without  removing  the  slag  the  required  amounts  of  carbon, 
silicon,  manganese,  etc.,  were  added.  That  there  was  no  return  of  phos- 
phorus to  the  steel  is  shown  by  the  analysis  of  the  final  product,  which 
was,  phosphorus  0.005%,  sulphur,  0.005%,  with  the  carbon  ranging  from 
0.05  to  1.50%,  and  the  manganese  and  silicon  as  desired. 

A  high  phosphorus  steel  is  sometimes  used  for  the  third  rail  in  an 
electric  railway,  as  phosphorus  will  increase  hardness  without  decreasing 
electric  conductivity  as  much  as  other  ingredients  would,  and  it  also 
decreases  the  purity  of  the  iron  less  than  any  other  material.  This 
gives  the  rails  the  necessary  hardness  and  purity  to  withstand  the 
abrasive  wear  caused  by  the  contact  shoes,  without  greatly  lessening  the 
conductivity. 

Phosphorus  in  cast-iron  reduces  the  melting  point,  makes  the  metal 
more  fluid,  and  prolongs  the  period  of  solidification.  This  is  made  useful 
in  such  work  as  art  castings,  where  a  detail  of  figure  is  of  more  importance 
than  strength,  as  the  metal  fills  every  minute  crevice  in  the  molds.  By 
keeping  the  metal  in  a  pasty  state  for  a  long  time,  or  retarding  solidifica- 
tion, the  phosphorus  allows  the  graphite  to  be  expelled  from  the  solid 
solution  and  occupy  spaces  between  the  particles  of  iron.  This  action 
causes  the  metal  to  expand  and  press  into  every  tiny  cavity  in  the  mold, 
and  the  higher  the  percentage  of  phosphorus  the  longer  will  the  solidifi- 
cation be  delayed.  Certain  chemical  conditions  caused  by  too  much  phos- 
phorus, too  little  silicon,  etc.,  might  overcome  this  by  exerting  a  tendency 
to  keep  the  carbon  in  the  combined  form.  A  decreased  shrinkage  because 
of  this  expansion  may  also  be  caused  when  the  phosphorus  separates  from 
its  solution  in  the  ferrite  and  forms  a  eutectic.  Phosphorus  also  increases 
the  tendency  toward  segregation. 

SULPHUR 

Sulphur  is  one  of  the  elements  of  the  earth  that  is  found  in  large  quan- 
tities in  the  free  state,  especially  in  volcanic  regions,  as  well  as  combined 
with  metals  in  the  form  of  sulphides.  It  is  given  off  from  the  fuels  used 
in  reducing  the  iron  ores  and  refining  steel,  and  at  the  higher  temperatures 
it  combines  with  the  oxygen  of  the  air  to  form  a  dioxide,  S02.  Part  of 


INGREDIENTS    OF    AND    MATERIALS   USED    IN    STEEL  81 

this  is  liable  to  be  trapped  in  the  metal  unless  precautions  are  taken  or 
slags  used  to  remove  the  sulphur. 

When  in  steel  in  the  form  of  sulphide,  it  causes  the  metal  to  crack, 
tear,  and  check  in  rolling,  forging,  heat  treating,  or  hot  working,  and, 
therefore,  the  term  of  "  hot-shortness "  has  been  applied  to  its  effect  on 
steel.  This  is  the  opposite  of  the  effect  of  phosphorus.  Its  effect  on 
the  properties  of  steel  when  cold  has  not  been  accurately  determined, 
but  it  seems  certain  that  the  effect  is  not  detrimental  to  any  extent. 

When  steel  is  heated  beyond  a  dull  red,  sulphur  in  the  sulphide  form 
is  said  to  cause  a  crystallization  to  take  place,  and  when  high  temper- 
atures are  reached  the  grain  becomes  very  coarse,  as  the  sulphur  is  dis- 
sociated and  forms  into  a  gas  that  diffuses  between  the  iron  crystals, 
thus  separating  them  arid  preventing  perfect  cohesion.  When  contrac- 
tion by  cooling  takes  place  this  may  cause  microscopic  cracks,  or  even 
cracks  large  enough  to  be  seen  by  the  naked  eye.  These,  of  course,  weaken 
the  metal.  Sulphur  and  phosphorus  increase  the  tendency  toward  segre- 
gation. 

Sulphur  takes  two  forms  in  steel,  one  of  which  is  sulphide  of  iron, 
and  the  other  sulphide  of  manganese.  Iron  sulphide  (FeS)  usually  forms 
when  the  sulphur  is  high  and  the  manganese  low,  as  sulphur  has  a  greater 
affinity  for  manganese  than  for  iron.  Until  the  manganese  is  satisfied, 
sulphide  of  iron  is  not  liable  to  occur,  and  this  latter  form  does  not  often 
occur  in  commercial  steels.  It  is  more  brittle  than  manganese  sulphide, 
and  at  the  proper  temperatures  for  rolling  steels  is  in  a  liquid  state,  so 
that  there  is  no  cohesion  between  it  and  the  molecules  of  steel.  Instead 
of  coming  together  in  drops,  as  manganese  sulphide  does,  it  spreads  out 
in  webs  or  sheets,  which  are  very  pale  in  color  and  usually  completely  sur- 
round the  manganese  sulphide.  These  cover  a  comparatively  large  area, 
and  the  effect  of  iron  sulphide  is  thus  very  injurious  to  steel,  as  it  is  very 
weak  and  liable  to  break  along  these  webs  or  sheets.  Owing  to  its  liquid 
state  iron  sulphide  is  very  liable  to  cause  trouble  at  the  rolling  tempera- 
tures, whether  this  temperature  be  used  for  rolling  or  when  forging,  weld- 
ing, or  heat-treating  the  steel. 

Sulphide  of  manganese  (MnS)  is  formed  by  the  uniting  of  manganese 
and  sulphur,  and  it  is  invariably  found  in  steel;  this  being  the  form  that 
sulphur  takes  in  all  the  good  grades  of  steel,  and  if  there  is  enough  man- 
ganese present  all  of  the  sulphur  in  the  metal  will  assume  this  form.  It 
usually  forms  in  globular  spots,  but  when  the  metal  is  rolled  or  hammered, 
these  generally  elongate  and  under  the  microscope  they  show  a  pale  state 
or  dove  gray  color. 

Opinion  differs  as  to  the  injurious  effect  of  manganese  sulphide  upon 
steel,  but,  however  this  may  be,  it  is  not  as  injurious  as  iron  sulphide. 
It  has  been  melted  in  coke-fired  assay  furnaces  that  would  not  melt  mild 


82  COMPOSITION    AND    HEAT-TREATMENT   OF    STEEL 

steel,  which  would  indicate  that  it  was  injurious  when  steel  was  heated 
to  comparatively  high  temperatures.  It  frequently  occurs  with  man- 
ganese silicate  (slag)  and  it  segregates  together  with  phosphide  of  iron 
in  the  form  of  ghosts.  In  this  case  it  may  be  very  injurious  to  steel, 
and  especially  so  where  the  sulphide  is  spread  out  into  threads  or  ribbons 
by  rolling  the  metal. 

Sulphur,  when  added  to  soft  cast  iron  that  is  low  in  sulphur,  increases 
the  strength  of  the  metal,  partly  by  closing  the  grain  and  partly  by  in- 
creasing the  combined  carbon.  Owing  to  this  tendency  to  increase  the 
combined  carbon  and  form  an  iron  carbide,  it  has  a  hardening  effect  on  the 
metal.  Its  effect  on  the  tensile  strength  of  steel  has  not  been  definitely 
settled,  but  up  to  0.10%  it  does  not  alter  the  elastic  ratio,  elongation,  or 
reduction  of  area  to  any  extent.  The  actual  percentage  of  sulphur  at  which 
steel  ceases  to  be  malleable  or  weldable  varies  with  other  ingredients. 
Each  increment  of  manganese  raises  it,  and  it  is  lowered  if  the  steel  ingots 
are  cast  too  hot. 

Attention  is  being  turned  to  the  effect  of  sulphur,  noted  in  the  pre- 
ceding paragraph,  and  the  old  theory  that  sulphur  should  be  reduced  to 
a  mere  trace  in  steel  is  beginning  to  be  doubted,  as  some  of  these  effects 
could  be  made  beneficial  if  the  injurious  effects  could  be  overcome.  Some 
recent  investigations  have  led  to  the  belief  that  the  oxides  are  the  real 
source  of  weakness  and  failures  in  steel,  and  if  these  can  be  removed, 
the  injurious  effects  of  sulphur  can  at  least  be  nullified,  with  the  probability 
of  its  being  made  beneficial. 

According  to  the  old  theory,  0.08%  of  sulphur  made  crucible  steel 
absolutely  worthless  for  welding,  forging,  rolling,  etc.,  but  I  have  recently 
seen  samples  of  crucible  steel  that  had  the  oxides  reduced  to  a  minimum, 
and  the  sulphur  at  0.08%,  that  were  forged  under  the  steam  hammer 
without  any  signs  of  checks.  A  piece  of  this  same  steel  which  con- 
tained 0.60%  of  carbon  was  welded  onto  machinery  steel  to  form  the 
cutting  edge  of  an  axe,  and  apparently  the  weld  was  perfect,  as  there  was 
no  signs  of  a  crack  when  it  was  ground  to  shape.  This  axe  was  stood 
on  an  anvil  with  the  cutting  edge  up,  and  given  20  blows  with  a  heavy 
sledge  before  the  edge  broke,  and  even  then  the  weld  was  not  harmed. 

Another  test  was  to  drift  a  hole  4  inches  in  diameter  in  stock  1 J  inches 
thick  and  4  inches  wide  without  destroying  the  drift.  In  still  another 
test  a  f-inch  set  stood  200  blows  from  a  12-pound  sledge  without  breaking. 
This  same  set  was  then  used  in  the  daily  work  at  the  mill  until  it  was 
worn  out,  and  it  outlasted  two  sets  made  from  stock  steel.  The  tensile 
strength  was  a  little  better  than  the  ordinary  in  this  high  sulphur  steel. 

The  sulphur  content  was  carried  still  higher  in  later  tests  and  it  was 
found  that  with  sulphur  up  to  0.13  per  cent,  no  injurious  effects  were 
apparent  in  the  steel  and  the  metal  did  not  develop  the  "  hot-shortness " 


INGREDIENTS    OF    AND    MATERIALS    USED    IN    STEEL  83 

that  every  one  heretofore  has  attributed  to  sulphur.  Above  a  sulphur 
content  of  0.13%  the  metal  began  to  show  signs  of  brittleness  and  was 
clearly  injured. 

With  steels  as  ordinarily  made  at  present  the  sulphur  should  not  exceed 
0.10%  for  any  use,  but  for  tool  making  or  other  uses  where  the  metal  has 
to  be  repeatedly  heated  and  cooled  this  should  not  be  over  0.03%,  and 
preferably  as  much  lower  as  possible.  Steel  as  now  made  would  be  much 
better  for  nearly  all  kinds  of  work  if  the  sulphur  could  be  reduced  to  a 
trace. 

OXYGEN,    HYDROGEN,    AND   NITROGEN 

Of  all  the  elements  that  enter  into  the  composition  of  the  earth's 
crust,  oxygen  forms  nearly  one-half,  or,  to  be  more  explicit,  47.29%. 
It  comprises  eight-ninths  of  water  and  about  one-fifth  of  the  air.  It 
occurs  also  in  combination  with  carbon  and  hydrogen,  and  with  carbon, 
hydrogen,  and  nitrogen.  Besides  this  it  forms  a  part  of  most  manufac- 
tured chemical  products.  The  iron  ores  that  are  chiefly  used  for  making 
iron  are  combinations  of  ferrite  and  oxygen.  At  the  higher  tempera- 
tures it  has  a  greater  or  lesser  affinity  for  and  unites  with  every  other 
elemental  substance  known,  except  fluorine,  helium,  neon,  argon,  krypton, 
and  xenon,  and  it  acts  readily  upon  a  large  number  of  compounds.  At 
the  ordinary  temperatures  oxygen  does  not  act  readily  upon  most  things. 
Its  simple  compounds  are  called  oxides,  and  these  usually  form  with  the 
production  of  heat.  One  of  the  elements  that  combine  with  it  at  low 
temperatures  is  iron,  and  this  is  coated  with  an  oxide  when  heated  to 
about  400°  F.,  or  at  nearly  any  temperature  in  the  presence  of  moisture. 

Hydrogen  is  the  lightest  substance  known,  and  like  oxygen  is  a  gas 
that  is  colorless,  tasteless,  and  odorless.  It  has  a  high  chemical  affinity 
for  oxygen,  and  is  a  good  reducing  agent.  It  forms  with  carbon  something 
like  200  combinations,  known  as  hydrocarbons.  At  a  red  heat  it  pene- 
trates iron  readily,  probably  forming  a  compound  with  it. 

Nitrogen,  owing  to  its  inactivity,  acts  principally  as  a  dilutent  of 
oxygen. 

These  three  gases  readily  dissolve  in  iron  or  steel  when  it  is  molten, 
but  as  it  solidifies  comes  out  of  the  state  of  solution,  and  then  much  the 
larger  part  passes  away.  A  portion,  however,  is  usually  entrapped,  and 
this  portion  if  segregated  in  large  bodies  causes  blow-holes,  gas  bubbles, 
etc.  Carbon  monoxide  gas  (CO),  which  may  be  generated  during  the 
solidification  period  by  a  reaction  of  the  oxide  of  iron  with  the  carbon 
when  carburizing,  is  also  a  cause  of  blow-holes.  These  blow-holes  are 
usually  removed  by  the  use  of  the  deoxidizers,  such  as  manganese,  silicon, 
aluminum,  etc.  Another  portion  of  these  gases,  however,  is  liable  to 
remain  in  the  steel  in  the  form  of  occluded  gases  and  oxides  that  are  just 


84  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

beginning  to  be  recognized  as  among  the  most  harmful  things  in  steel; 
oxygen  probably  being  the  most  weakening  element  that  can  be  left  in 
steel,  with  hydrogen  and  nitrogen  closely  following. 

As  evidence  of  this,  Bessemer  steel,  which  is  purified  by  blowing  air 
through  it,  is  the  poorest  and  weakest  of  steels;  while  open-hearth  steel, 
which  is  purified  without  this  blast  of  air,  but  is  not  protected  from  the 
air  striking  the  surface  of  the  bath,  comes  next;  and  crucible  steel  being 
protected  from  air  by  the  melting  process  taking  place  in  a  closed  pot, 
is  the  strongest  and  finest  grained  of  all  the  steels,  except  those  made 
in  the  electric  furnace,  and  this  is  also  protected  from  the  air.  Another 
proof  is  the  added  static  and  dynamic  strength,  wearing  qualities,  etc., 
given  to  steels,  by  such  elements  as  vanadium,  titanium,  etc.,  when  they 
are  used  to  cleanse  the  metal  of  these  gases. 

Oxide  occurs  in  very  small  black  specks  throughout  the  metal  and 
can  only  be  seen  when  the  surface  has  been  perfectly  polished  and  mag- 
nified at  least  one  thousand  times.  These  are  invariably  found  in  steels 
that  produce  blisters  when  pickling,  and  this  leads  to  the  conclusion  that 
the  blisters  were  formed  by  the  reduction  of  oxide  by  the  nascent  hydro- 
gen evolved  during  the  pickling  process.  High-carbon  steel  rods  that  con- 
tain the  same  impurity  occasionally  fracture  in  the  pickling  bath  and 
doubtless  the  same  pressure  that  blows  a  blister  in  mild  steel  will  cause 
a  rupture  in  hard  steel. 

Owing  to  the  gaseous  nature  of  oxygen,  and  the  fact  that  the  drillings 
must  be  very  fine,  it  is  difficult  to  analyze  steel  for  the  oxygen  content. 
A  series  of  tests,  however,  was  carried  out  by  E.  F.  Law,  of  London,  by 
cutting  a  piece  from  each  of  eleven  bars  of  acid  and  basic  Bessemer  steel 
that  contained  from  0.10  to  0.18%  of  carbon,  and  only  a  trace  of  silicon. 
Each  piece  was  then  rolled  into  24  sheets  which  were  pickled  and  annealed 
by  the  usual  process.  An  adjacent  piece  of  the  bar  was  analyzed,  exam- 
ined with  a  microscope,  and  the  oxygen  determined.  The  result  of  these 
tests  was  as  follows:  (See  table  on  page  85.) 

An  examination  of  the  table  will  show  that  as  the  oxygen  content 
increased  the  number  of  blistered  sheets  increased,  while  the  percentage 
of  sulphur  seemed  to  have  no  effect  on  the  blistering;  the  set  containing 
19  blistered  sheets  only  showing  0.071%  of  sulphur,  while  the  set  of  sheets 
that  did  not  blister  at  all  contained  0.076,  0.069,  and  0.061%  of  sulphur, 
respectively.  By  way  of  comparison  a  piece  of  basic  Bessemer  steel 
was  analyzed  just  before  the  ferro-manganese  was  added,  and  this  showed 
0.062%  of  oxygen.  The  results  shown  here  seem  to  forcibly  confirm  the 
oxide  theory. 

It  might  appear  at  first  sight  that  the  quantities  present  are  extremely 
small,  but  in  making  comparisons  we  should  not  consider  alone  the  amount 
of  the  elements  present,  but  also  the  combinations  of  these  elements  that 


INGREDIENTS  OF  AND  MATERIALS  USED  IN  STEEL  85 

TABLE    SHOWING   EFFECT   OF    OXYGEN    ON    BLISTERING 


Kind  of 

Analysis 

Microscopical 

Sheets  in  24 
that 

Percentages 

Steel 

s 

P 

Mn 

Appearance 

Blistered 

Oxygen 

Acid  

.061 

.049 

.340 

Very  good 

0 

.021 

Basic     .          .    . 

069 

.034 

.385 

Good 

0 

.021 

Acid 

076 

070 

.350 

Good 

o 

.022 

Basic  

.101 

.126 

.475 

Fair 

4 

.025 

Basic    .  .        .... 

.080 

.066 

.430 

Moderate 

6 

.026 

Acid 

106 

.188 

.320 

Bad 

7 

.026 

Basic 

079 

098 

.440 

Bad 

7 

027 

Basic  

.045 

.075 

.473 

Bad 

8 

.034 

Acid 

061 

.081 

350 

Bad 

9 

032 

Basic  

.080 

.068 

.450 

Bad 

12 

.030 

Basic  

.071 

.090 

480 

Very  bad 

19 

046 

influence  the  quality  of  the  steel.  Thus,  we  speak  of  0.05%  of  sulphur, 
when  in  reality  it  is  0.13%  of  manganese  sulphide  that  affects  the  quality 
of  the  steel.  Oxygen  has  only  half  the  atomic  weight  of  sulphur,  and 
is  capable  of  forming  larger  quantities  of  compounds,  therefore  it  exerts  a 
greater  influence.  Thus,  where  0.05%  of  sulphur  corresponds  to  0.13%  of 
manganese  sulphide,  0.05%  of  oxygen  corresponds  to  0.22%  of  ferrous 
oxide. 

Another  fact  brought  out  in  these  tests  is  that  the  amount  of  oxide 
visible  under  the  microscope  was  much  less  than  would  be  expected  from 
the  amount  actually  found  by  chemical  analysis,  and  this  might  be  ac- 
counted for  on  the  theory  that  a  considerable  quantity  of  oxide  was  in 
solution  in  the  steel  surrounding  the  black  oxide  spots.  The  oxide  show- 
ing on  the  surface  of  a  polished  piece  was  also  reduced  by  the  aid  of  hydro- 
gen and  an  electric  current,  and  the  pits  thus  formed  occupied  a  much 
larger  area  than  the  spots  of  oxide  seen  by  the  microscope. 

Steels  containing  oxides  also  apparently  rust  much  quicker  than  those 
free  from  them,  and  with  two  pieces  placed  side  by  side  the  oxide  steel 
will  show  rusting  long  before  the  other,  while  in  dilute  acid  solutions 
steels  containing  oxides  corrode  more  easily  and  much  faster  than  those 
free  from  oxides.  The  same  is  true  regarding  the  other  impurities  in 
steel  and  this  has  led  to  the  production  of  a  metal  called  " Ingot  iron," 
in  which  the  total  impurities,  except  carbon,  have  been  reduced  to  from 
0.05  to  0.08%  and  the  carbon  content  to  0.02%.  A  typical  analysis  showed 
carbon  0.02%;  manganese,  0.01%;  sulphur,  0.02%;  oxygen,  0.03%,  and 
phosphorus  and  silicon  a  trace. 

In  the  making  of  this  metal  the  theory  that  ferro-manganese  was  needed 
to  produce  a  workable  metal  in  the  hot  condition  was  doubted,  and  the 


86  COMPOSITION   AND    HEAT-TREATMENT   OF    STEEL 

usual  ferro-manganese  decarburizer  was  omitted.  Open-hearth  furnaces 
are  worked  entirely  on  cold  pig  iron  low  in  silicon  and  sulphur,  and  with 
the  phosphorus  limited  to  the  content  for  Bessemer  working.  An  active 
basic  slag  is  maintained  that  is  composed  of  limestone  and  fluorspur,  with 
a  comparatively  large  amount  of  the  latter  flux  to  prevent  the  phosphorus 
from  returning  to  the  metal  at  the  high  temperature  of  3000°  to  3100°  F., 
that  is  maintained  toward  the  end  of  the  process.  A  fairly  large  propor- 
tion of  scrap  is  charged  in  the  form  of  open-hearth  mill  scrap  and  low- 
carbon  steel  turnings,  the  larger  part  being  of  the  latter.  When  sufficient 
mill  scale  can  be  obtained  it  is  substituted  for  ore  in  the  charge. 
i  The  removal  of  oxygen,  probably  in  the  metal  in  the  form  of  oxides, 
is  most  important,  and  instead  of  manganese,  ferro-silicon,  or  an  equiv- 
alent material,  is  added  to  the  bath  to  remove  the  oxides,  while  the  other 
gases  are  removed  by  adding  below  0.10%  of  granular  aluminum  in  the 
ladle.  The  time  consumed  for  each  charge  is  about  10  hours,  and  the 
boiling  is  carried  to  a  high  temperature  to  thoroughly  oxidize  the  impuri- 
ties. This  brings  the  temperature  very  high  in  the  final  stages,  owing 
to  the  higher  melting  point  of  the  purer  materials.  If  there  is  too  much 
oxygen  in  the  steel  it  is  liable  to  cause  it  to  crack  on  the  edges  when  roll- 
ing, owing  to  its  creating  a  red-shortness. 

COPPER 

Copper  is  a  widely  distributed  element  of  the  earth's  crust,  and  occurs 
in  large  quantities;  sometimes  in  the  uncombined  condition,  such  as  the 
native  copper  of  the  Lake  Superior  regions.  It  is  very  malleable  and 
tenacious.  In  most  of  the  copper  ores  used,  sulphur  and  iron  occurs,  and 
in  some  of  the  iron  ores  used  for  making  steel,  copper  occurs.  A  few  con- 
tain as  high  as  1%  of  copper,  and  some  of  the  Bessemer  and  open-hearth 
steels  contain  from  0.30  to  0.50%  of  this  metal.  That  copper  alloys 
perfectly  with  all  steels  and  does  not  segregate  until  above  4%  has  been 
added  is  a  well-established  fact. 

Copper  can  be  alloyed  in  all  proportions,  with  iron  containing  0.15% 
of  carbon,  and  with  0.09%  of  sulphur  added  to  this  no  segregation  will 
occur  until  7.70%  of  copper  has  been  added.  With  the  sulphur  low  and 
the  carbon  at  0.20%  no  pronounced  segregation  appears  until  a  copper 
content  of  40%  is  reached,  while  with  0.40%  of  carbon  it  occurs  with 
a  copper  content  of  about  30%.;  with  carbon  0.60%,  at  20%  copper; 
with  carbon  0.80%,  at  12%  copper;  and  with  the  carbon  at  1%,  copper 
segregation  is  liable  to  occur  when  the  copper  is  8%.  This,  however,  is 
only  a  general  rule,  and  it  may  be  varied  greatly  by  the  various  other 
ingredients  and  methods  of  making  the  steel.  As  the  best  results  seem 
to  be  obtained  when  copper  is  kept  below  5%,  segregation  will  not  be 
much  of  a  factor  in  copper  steel. 


INGREDIENTS  OF  AND   MATERIALS  USED  IN  STEEL  87 

Hard  and  soft  steels  with  a  percentage  of  copper  as  one  of  the  ingre- 
dients have  been  used  for  many  purposes  with  the  usual  number  of  fail- 
ures, but  these  failures  have  always  been  traced  to  other  ingredients 
and  none  to  the  copper  contents.  Crank-shafts  for  the  United  States* 
battleships  and  gun  tubes  for  6-inch  guns,  have  been  made  out  of  steel 
containing  0.57%  copper,  and  they  stood  successfully  all  of  the  tests 
required  by  the  Government. 

Commercially  steels  containing  over  4%  of  copper  cannot  be  rolled 
and  forged  unless  the  percentage  of  carbon  is  very  low,  owing  to  its  hard- 
ening effect  and  the  consequent  brittleness  it  gives  to  the  metal.  With 
percentages  up  to  4,  the  copper  all  goes  into  solution  in  the  iron,  but 
above  that,  saturation  begins  to  occur.  The  point  at  which  saturation 
begins  appears  to  be  between  4  and  8%;  it  being  lowered  as  the  carbon 
content  is  increased.  When  the  copper  content  is  increased  to  above 
8%  free  copper  occurs;  in  a  fibrous  form  in  the  soft  or  semi-soft  steels, 
and  in  nodules  in  the  higher  carbon  steel. 

When  there  is  enough  sulphur  in  the  steel,  it  will  form  with  the  copper 
a  copper  sulphide,  according  to  the  formula  (Cu2S),  but  if  there  is  an  excess 
of  copper  it  will  combine  with  the  iron.  Steels  containing  copper  and 
copper  sulphide  have  an  irregular  structure,  as  regards  the  size  and  join- 
ing together  of  the  ferrite  crystals,  as  these  imbricate  with  one  another 
with  curved  junctions.  This  gives  the  metal  a  higher  strength  than  that 
of  steel  without  copper. 

Copper  and  copper-sulphide  principally  distribute  themselves  between 
the  crystals  of  ferrite,  which  they  envelop.  They  also  cause  the  quantity 
of  pearlite  to  increase  and  the  grains  of  this  to  assume  a  finer  structure 
and  permeate  the  metal  more  and  more  with  each  increase  in  copper. 
In  fact,  the  structure  so  closely  approaches  the  martensitic  form  that 
it  has  been  mistaken  for  this  in  some  instances,  and  in  a  7%  copper  steel 
threads  of  cementite  and  of  pearlite  appeared.  In  this  way  they  inten- 
sify the  iron  carbide  and  give  to  the  metal  a  greater  hardness  as  well 
as  enable  it  to  be  hardened  more  easily  when  heating  and  quenching. 
Copper  also  lowers  the  recalescent  point  from  100  to  150P  F.  below  that 
of  ordinary  steels,  but  it  never  brings  this  below  800°  F.  In  this  it  about 
equals  high-carbon  steel.  The  1  to  5%  copper  steels  that  are  liable  to 
become  commercially  successful  should  be  quenched  in  water  from  about 
1325°  F.  or  in  oil. 

It  is  possible  to  find  traces  of  copper  sulphide  in  metal  that  contains 
only  7%  of  iron  and  0.025%  of  sulphur.  As  a  small  amount  of  iron  in 
solution  in  copper  makes  copper  harder,  this  might  suggest  the  idea  of 
strengthening  copper  or  copper  alloys  with  iron. 

Copper  increases  the  hardness  of  steel,  as  the  copper  content  increases. 


88  COMPOSITION  AND   HEAT-TREATMENT   OF   STEEL 

When  the  carbon  content  is  low  it  has  a  greater -effect  than  when  it  is 
high;  in  some  cases  almost  doubling  the  Brinnell  hardness,  and  it  reached 
its  maximum  increase  in  one  series  of  tests  at  from  10  to  15%  copper. 
It  does  not  give  any  color  to  steel  until  8%  has  been  passed. 

With  the  carbon  content  high,  copper  steel  is  difficult  to  work  mechan- 
ically, but  it  can  be  easily  cast  into  the  shapes  desired.  If,  however,  the 
carbon  is  kept  below  0.50%,  steels  containing  as  high  as  4%  of  copper 
can  be  easily  and  successfully  rolled  and  forged,  and  the  heat  treatment 
made  a  less  delicate  operation.  Such  steels  seem  to  have  a  future  as  they 
have  a  greater  tensile  strength  and  elastic  limit  than  the  same  steel 
without  copper;  a  better  elongation  and  contraction;  more  resiliency; 
a  greater  resistance  to  shock  and  torsional  strains;  a  greater  hardness 
without  loss  of  ductility  and  a  finer  grain.  The  copper  steels  closely 
resemble  nickel  or  chromium  steel,  and  follow  the  same  laws  as  to  their 
increases  of  strength  for  each  increase  of  percentage,  but  they  are  said  to 
possess  a  higher  elastic  limit  and  maximum  strength  than  nickel  steel,  as 
well  as  greater  dynamic  strengths.  Copper  has  a  more  active  influence 
on  steel  than  nickel  or  manganese,  and  nearly  approximating  chromium, 
molybdenum,  and  vanadium,  and  it  is  a  cheaper  alloying  material  than 
these. 

Copper  steels  as  rolled  show  greater  tensile  strength  with  each 
increase  of  copper,  and  this  is  more  manifest  with  the  lower  carbon  per- 
centages, but  it  is  not  dependable  in  this  state.  Annealing  corrects 
this  to  a  large  extent,  but  does  not  leave  the  metal  much  if  any  stronger 
than  the  ordinary  steel.  Hardening  and  tempering  after  this,  how- 
ever, more  than  doubles  the  tensile  strength  and  elastic  limit,  and 
brings  the  latter  up  close  to  the  former  with  a  good  percentage  of  con- 
traction. This  would  seem  to  indicate  that  if  copper  steels  were  well 
made  they  would  be  able  to  withstand  shock,  torsional,  alternating,  or 
vibrational  strains,  as  well  as  the  high-grade  steels  of  the  present  day, 
and,  owing  to  the  comparative  cheapness  of  copper,  they  could  be  pro- 
duced cheaper. 

Some  corrosion  tests  were  carried  on  that  showed  that  corrosion  was 
lower  by  something  like  100%  in  copper  steel  than  in  steels  that  contained 
no  copper.  The  electrical  resistance  is  also  increased  in  steels  containing 
copper,  and  reaches  its  maximum  in  a  0.15%  carbon  steel  at  2%  of  copper; 
in  a  0.7%  carbon  steel  at  0.5%  copper,  and  in  a  1.7%  carbon  steel  at 
0.35%  copper. 

ARSENIC   AND    THE   ANALOGOUS    ELEMENTS   ANTIMONY   AND    BISMUTH 

Phosphorus,  arsenic,  antimony,  and  bismuth  all  belong  to  the  same 
chemical  group,  and  in  general  form  compounds  of  the  same  character 


INGREDIENTS  OF  AND  MATERIALS  USED  IN  STEEL  89 

and  of  similar  composition.  Like  nitrogen  they  unite  with  metals  to 
form  binary  compounds,  called  phosphides,  arsenides,  and  antimonides. 
They  all  form  two  oxides,  which  contain  2  atoms  of  the  above-named 
elements  to  3  atoms  and  5  atoms  of  oxygen.  Of  these  elements  phos- 
phorus occurs  most  abundantly  in  nature:  arsenic  and  antimony  next, 
arid  bismuth  last.  The  last  three  occur  sometimes  in  the  uricombined 
state,  but  phosphorus  always  occurs  in  combination  with  other  elements. 

Many  steels  contain  an  appreciable  percentage  of  arsenic,  as  it  com- 
bines with  iron  in  forms  that  are  similar  to  the  sulphide  which  it  fre- 
quently accompanies.  The  arsenides,  which  are  its  compounds  with 
metals,  occur  very  widely  distributed,  and  often  accompany  the  sulphides 
to  which  they  are  similar.  The  most  common  compound  of  this  kind  has 
the  composition  FeAsS,  and  may,  therefore,  be  regarded  as  iron  pyrites 
(FeS2),  in  which  one  atom  of  arsenic  has  been  substituted  for  one  atom 
of  sulphur.  Simple  compounds  of  pyrite  and  arsenic  occur  that  are  anal- 
ogous to  the  sulphide  FeS2,  and  combinations  of  sulphur  and  arsenic 
form  into  sulphides. 

When  steel  contains  an  appreciable  percentage  of  arsenic  it  will  give 
off  an  odor  similar  to  garlic  when  heated  to  a  red  heat,  and  this  odor  may 
become  very  intense  at  a  welding  or  forging  heat.  As  an  element  it  is 
not  poisonous,  but  when  oxidized  it  may  become  extremely  so  and  it 
is  easily  oxidized. 

If  the  arsenic  in  commercial  steel  does  not  exceed  0.20%  it  does  not 
have  any  material  effect  upon  the  mechanical  properties,  as  the  elongation 
and  reduction  of  area  are  not  changed  and  the  tenacity  is  but  slightly 
increased.  This  leaves  the  bending  properties  unchanged  at  ordinary 
temperature.  Above  0.20%  the  strength  of  steel  is  increased  and  the 
toughness  decreased  with  each  increase  in  the  percentage  of  arsenic  until 
4%  is  reached,  when  the  elongation  and  reduction  of  area  become  nil 
and  the  steel  becomes  very  brittle.  Even  with  4%,  however,  it  does  not 
affect  the  hot  working  of  the  metal,  and  it  can  be  alloyed  with  iron  in 
proportions  as  high  as  56%  under  certain  conditions  of  mixing.  These 
conditions,  however,  are  difficult  to  fulfil. 

By  ordinary  methods  attempts  have  been  made  to  produce  alloys 
in  various  proportions  up  to  10%  of  arsenic,  but  when  analyzed  the  sample 
showed  that  the  maximum  of  arsenic  taken  up  and  retained  by  the  iron 
was  about  4%,  this  appearing  to  be  about  the  largest  amount  that  could 
be  commercially  added  to  steel.  While  steels  with  the  higher  percentage 
of  arsenic  are  brittle,  no  special  difficulty  is  met  with  in  machining  them 
with  any  percentage  of  arsenic. 

Owing  to  the  fact  that  arsenic,  when  present  in  acid  pickling  solutions, 
causes  a  marked  reduction  in  the  rate  of  attack  by  the  acid,  it  was  thought 
that  if  the  arsenic  was  added  to  the  iron  it  might  resist  the  attacks  of 


90  COMPOSITION    AND   HEAT-TREATMENT   OF   STEEL 

corrosion  and  become  more  durable.  Numerous  tests  that  were  made, 
however,  show  no  appreciable  difference  in  the  non-corrosive  qualities 
of  iron  and  steel  that  contained  arsenic  and  those  of  the  ordinary 
brand. 

Any  benefits  derived  from  alloys  of  arsenic  with  iron  or  steel  will 
probably  be  in  connection  with  their  magnetic  properties,  as  some  very 
interesting  results  have  been  obtained  along  this  line.  It  alloys  with 
iron  practically  in  proportions  of  the  solid  mixtures,  up  to  an  arsenic 
content  of  4%.  With  each  increase  of  arsenic  in  steel  up  to  5%,  the  mag- 
netic qualities  of  iron  are  made  better  and  the  arsenic  alloys  are  on  an 
equality  with  the  best  electrolytic  material  known  in  respect  to  mag- 
netic permeability.  When  the  metal  is  heated  to  1250°  F.  and  slowly 
cooled,  so  as  to  allow  the  grain  to  become  normal  and  the  forging  or  roll- 
ing strains  to  be  removed,  the  metal  shows  a  decided  improvement.  A 
second  heating  to  1800°  F.,  with  slow  cooling,  improves  the  quality  in 
the  lower  ranges  of  the  magnetic  forces,  but  there  is  a  falling  off  in  the 
upper  ranges  of  the  curve.  Quenching  from  1650°  F.  shows  no  harden- 
ing and  but  slight  changes  in  the  magnetization  curves.  Arsenic  added 
to  iron  imparts  to  the  alloy  magnetic  qualities  excelling  those  of  the  purest 
iron,  and  at  least  equaling  those  of  the  best  material  from  which  data 
is  obtainable. 

ANTIMONY  may  be  added  to  iron  in  quite  large  percentages,  but  above 
a  content  of  1%  the  metal  is  not  forgeable,  and  only  then  with  difficulty. 
It  renders  the  metal  brittle  so  that  it  is  practically  worthless,  and  it  is 
of  a  lower  grade  magnetically  than  the  ordinary  electrolytic  iron.  Thus 
while  antimony  is  in  the  same  chemical  group  as  arsenic,  it  makes  iron 
products  that  are  difficult  to  work  and  have  no  apparent  value  as  a  mag- 
netic material.  Antimony  is  useful  in  the  non-ferrous  alloys  for  the 
hardening  effect  it  gives,  and  that  it  expands  when  solidifying  makes  it 
valuable  for  such  uses  as  type  casting.  These  same  properties  make 
it  detrimental  to  iron  and  steel  products,  and  luckily  it  does  not  appear 
in  the  crude  materials  used  for  making  these. 

BISMUTH,  like  antimony,  does  not  occur  in  combination  with  iron  or 
in  the  products  used  for  producing  the  iron  ore  when  refining  it  into  steel, 
conseqently  it  does  not  have  to  be  removed  as  an  impurity.  To  a  greater 
degree  than  antimony  it  has  the  property  of  expansion  when  passing  from 
the  liquid  to  the  solid  state,  and  therefore  it  is  useful  in  non-ferrous 
alloys. 

When  2%  of  bismuth,  the  most  diamagnetic  element  known,  was 
added  to  iron,  it  improved  the  already  high  magnetic  quality  of  the  pure 
iron.  The  density  values  reached  exceed  those  obtained  from  any  of 
several  hundred  other  different  alloys  that  have  been  tested.  How  much 
bismuth  remained  in  the  metal  after  adding  the  2%,  however,  was  not 


INGREDIENTS    OF    AND    MATERIALS    USED    IN    STEEL  91 

known.  With  bismuth  alloys  there  is  but  little  increase  in  electrical 
resistance.  Arsenic  and  antimony,  however,  give  a  decided  increase  in 
resistance  to  iron,  and  in  some  cases  this  was  from  62  to  67%. 


BORON 

In  nature  boron  chiefly  occurs  in  the  form  of  boric  acid,  or  as  salts 
of  this  acid,  such  as  borax,  a  sodium  salt,  or  two  calcium  salts.  It  belongs 
to  the  same  chemical  family  as  aluminum,  and  is  very  similar  to  it  in 
the  composition  of  its  compounds,  but  its  oxide  is  acidic,  while  the  oxide 
of  aluminum  is  usually  basic.  In  some  respects  it  resembles  the  members  of 
the  family  to  which  nitrogen  and  phosphorus  belong.  It  has  a  strong 
affinity  for  nitrogen,  especially  at  the  higher  temperatures,  and  also  com- 
bines readily  with  sulphur  and  chlorine.  Some  boron  crystals  con- 
tain carbon  and  aluminum,  which  seem  to  be  in  combination  with  the 
boron. 

Ferro-boron  can  be  prepared  from  borate  of  lime,  in  the  electric  fur- 
nace, without  any  special  difficulty,  and  the  above  data  would  suggest 
that  boron  might  have  some  qualities  that  would  be  beneficial  to  steel, 
but  very  little  in  the  way  of  investigation  has  so  far  been  done.  What 
little  has  been  done  would  indicate  that  boron  acts  like  carbon  in  many 
respects,  especially  in  adding  hardness  to  the  metal. 

In  some  recent  tests  which  were  made  on  steel  containing  0.20%  of 
carbon  and  0.20,  0.50,  0.80,  1,  and  2%  of  boron,  the  Brinell  hardness  of 
the  samples  tested  and  quenched  at  1460°  F.  was  three  times  that  of  the 
annealed  pieces,  and  equal  to  that  of  high-carbon  steel  similarly  treated. 
Notwithstanding  this  the  hardened  samples  could  be  easily  filed,  sawed,  or 
machined,  while  0.87%  carbon  steel,  similarly  treated,  could  not  be 
scratched  except  with  an  emery  wheel. 

This  is  adding  evidence  to  the  statement  that  has  been  made  several 
times,  but  disputed  by  some,  namely :  that  hardness  is  not  the  same  thing  as 
the  ease  or  difficulty  with  which  steel  can  be  machined  with  cutting  tools. 
The  tests  also  show  that  boron  confers  upon  steel  the  property  of  temper- 
ing; but  a  tempering  that  is  very  different  from  that  conferred  upon  the 
metal  by  carbon,  in  that  it  increases  the  tensile  strength  and  elastic  limit, 
without  materially  increasing  the  toughness  or  hardness  to  machine. 
On  the  other  hand,  the  ability  to  withstand  shock  tests  was  doubled  by 
quenching,  and  the  elastic  limit  was  brought  up  close  to  the  tensile  strength. 

In  heating  boron  steels  they  show  a  definite  emission  of  heat  at  2100° 
F.,  which  resembles  the  recalescent  point  in  high-carbon  steel.  Slightly 
marked  critical  points  appear  at  1900°,  1525°,  1350°,  and  1225°  F.  The 
three  latter  are  about  the  temperature  of  the  points  Ar3,  Ar2,  and  Arl 
of  mild  steel.  The  point  at  1240°  F.  is  definitely  shown  in  carbon  steel, 


92  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

but  when  boron  is  added  and  the  steel  heated,  this  point  almost  entirely 
disappears,  and  is  replaced  by  the  point  at  2100°  F. 

Boron  may  be  said  to  give  steel  a  hardness  that  increases  its  strength, 
up  to  a  content  of  2%  of  boron,  providing  the  carbon  is  kept  below  0.2%, 
but  beyond  a  content  of  2%  boron  or  0.2%  carbon,  the  metal  becomes 
so  brittle  that  it  is  weakened  and  easily  powdered  under  a  hammer.  Other 
elements  might  be  found,  with  further  investigations,  that  would  over- 
come this  brittleness  and  make  boron  more  useful  for  special  alloys  of 
steel. 

Microscopical  examinations  show  intense  black  spots  in  boron  steels 
that  are  polished  and  etched,  first  with  picric  acid  and  then  with  picrate 
of  sodium.  These  increase  in  quantity  with  each  increase  in  the  -per- 
centage of  boron.  These  spots  may  be  a  combination  of  boron-iron;  a 
solid  solution  of  boron-iron  containing  a  very  low  percentage  of  boron;  a 
borocarbide  of  iron,  or  a  boride  of  carbon.  In  specimens  thus  treated  the 
ferrite  appears  white,  the  pearlite  grayish,  and  the  special  constituent 
very  black. 

On  annealing,  the  volume  of  pearlite  increases  and  the  special  con- 
stituent disappears  by  forming  a  eutectic  with  the  ferrite  that  at  times 
is  strongly  marked.  By  annealing  in  the  presence  of  oxide  of  iron,  so 
as  to  decarburize  the  metal,  the  pearlite  is  first  caused  to  disappear  and 
then  the  special  constituent. 

In  carbonizing  the  special  constituent  is  not  increased  by  case-harden- 
ing, although  at  the  edges  a  layer  of  pearlite  is  found  and  this  is  thinner 
if  the  metal  does  not  contain  boron.  This  would  indicate  that  the  pene- 
tration of  carbon  is  delayed  by  boron,  and  that  the  amount  of  the  special 
constituent  depends  upon  the  percentage  of  boron,  and  is  independent  of 
the  carbon  content. 

In  the  quenched  steels,  the  special  constituent  was  hardly  discernible 
when  the  percentage  of  boron  was  below  0.50,  but  large  quantities  appeared 
in  the  steels  with  the  higher  percentages  of  boron.  This  was  not  altered 
even  when  the  quenching  was  carried  to  2200°  F.  The  percentage  of 
carbon  increases  the  solubility  of  the  special  constituent,  and  the  higher 
the  percentage  of  boron  the  less  easily  does  it  dissolve. 

The  above  data  probably  indicates  that  the  black  spots  were  a  boro- 
carbide of  iron,  and  its  percentage  of  carbon  very  low;  otherwise  a  phenom- 
ena would  occur  similar  to  that  brought  out  in  the  investigations  of  the 
vanadium  steels,  i.e.,  as  the  boron  increased  the  pearlite  would  diminish; 
but  in  these  steels  the  special  constituent  continues  to  increase. 

Boron  steels  are  very  weak  and  brittle  in  the  normal  state,  and,  if 
heated  to  a  very  high  temperature,  crumble  when  forged  or  rolled.  But 
if  heated  to  a  dull  red  they  can  easily  be  forged,  rolled,  or  otherwise  mechan- 
ically worked,  as  they  act  much  like  soft  steel.  This  will  make  them  use- 


INGREDIENTS   OF   AND    MATERIALS   USED    IN   STEEL  93 

less  in  the  raw  state,  but  after  quenching  they  possess  a  high  tensile 
strength,  a  very  high  elastic  limit,  and  are  not  any  more  brittle  than  the 
special  steels  that  are  in  actual  use  at  present. 

Borax  is  a  sodium  salt  from  which  amorphous  boron,  in  almost  pure 
form,  can  be  obtained  by  heating  with  magnesium  powder.  It  has  been 
used  by  many  misinformed  people  as  part  of  a  mixture  for  carbonizing 
steel,  or  in  a  special  compound  for  hardening  it,  but  they  have  never 
given  any  good  reason  for  its  use  or  shown  any  results  that  were  obtained 
thereby.  It,  like  boron,  retards  the  penetration  of  carbon,  but  when  used 
in  a  quenching  bath  may  aid  in  producing  a  greater  hardness,  or  prevent- 
ing the  metal  from  cracking  or  checking.  Common  table  salt  (NaCl), 
however,  gives  much  better  results,  and  is  easier  obtained  and  cheaper. 
Therefore  borax  is  not  useful  here ;  its  chief  value  is  as  a  flux  in  welding. 


TANTALUM 

Tantalum  is  one  of  the  rare  elements.  It  is  never  found  free  in  nature, 
but  occurs  in  combination  in  the  minerals  columbite  and  tantalite,  accom- 
panied by  niobium.  In  chemistry  it  is  grouped  with  vanadium,  niobium, 
and  didymium,  all  of  which  are  rare.  Its  rareness,  and  consequent  cost, 
has  prohibited  it  from  being  experimented  with  to  any  extent,  but  one 
series  of  tests  that  was  conducted  appeared  to  prove  that  it  had  a  harden- 
ing effect  upon  steel,  similar  to  that  exerted  by  tungsten  and  molybdenum, 
and  to  a  certain  extent  gave  promise  of  being  beneficial  for  high-speed 
steel  tools. 

In  all  of  the  eight  tests  made,  the  tantalum  which  varied  from  0.42  to 
1.69%  increased  the  tensile  strength,  elastic  limit,  elongation,  and  reduc- 
tion of  area  over  that  of  the  same  steel  without  tantalum,  but  when  nickel 
or  chromium  was  added  in  place  of  the  tantalum,  the  same  strengths  were 
obtained  and  in  one  case  1.10%  of  chromium  gave  about  10%  greater 
strength  than  0.43%  of  tantalum.  The  greatest  increases  in  strength 
were  obtained  with  the  smallest  percentages  of  tantalum. 

Under  the  microscope  a  dark  constituent  appeared  that  was  greater 
in  quantity  as  the  percentage  of  tantalum  increased,  and  this  occurred 
in  a  finely  granular  matrix  that  in  the  hardened  specimens  seemed  to 
be  martensitic  and  more  or  less  homogeneous. 

From  the  results  obtained  and  its  similarity  to  vanadium  the  sugges- 
tion occurs  that  it  acts  on  steel  as  a  scavenger  similar  to  this,  and  the 
best  results  would  be  obtained  in  the  quaternary  steels,  but  no  evidence 
has  been  submitted  to  prove  that  it  is  any  better,  or  even  as  good  as  the 
alloying  materials  already  in  use,  and  which  are  much  cheaper.  It  is 
also  very  difficult  to  separate  it  from  niobium,  with  which  it  is  always 
combined,  and  this  element  is  liable  to  cause  erratic  results  in  steel. 


94  COMPOSITION    AND   HEAT-TREATMENT   OF   STEEL 


PLATINUM 

Platinum  occurs  in  nature  associated  with  five  other  elements,  more  rare 
than  itself.  They  are  divided  into  two  chemical  sub-groups  commonly  called 
the  platinum  metals.  These  nearly  always  occur  in  an  alloy  in  which 
the  platinum  is  from  50  to  80%,  while  the  other  five  compose  the  balance. 

It  forms  two  oxides  and  two  sulphides.  It  is  very  ductile  and  is  a 
grayish-white  metal  that  looks  like  steel.  It  can  be  welded  at  a  white 
heat.  An  alloy  of  platinum  and  silicon  can  be  formed  by  bringing 
it  in  contact  with  red-hot  charcoal  and  silicon  dioxide.  Nitric,  hydro- 
chloric, or  sulphuric  acid  will  not  dissolve  it.  Platinum,  when  finely 
divided,  has  an  extraordinary  power  of  condensing  gases  upon  its  surface; 
for  instance,  it  absorbs  200  times  its  own  volume  of  oxygen,  also  other 
gases  similarly.  The  oxygen  is  then  in  the  active  condition,  and  oxidiz- 
able  materials  are  easily  oxidized  when  brought  into  contact  with  it. 
Thus  when  sulphur  dioxide  and  oxygen  flow  together  over  spongy  plati- 
num, or  even  the  compact  metal,  they  form  sulphur  trioxide  by  a  unity 
of  the  two  gases,  or  when  hydrogen  flows  against  the  spongy  platinum 
it  takes  fire. 

Iridium  belongs  to  the  same  chemical  group  and,  when  this  is  alloyed 
with  platinum  in  the  proportions  of  1  to  9  respectively,  it  reduces  the 
malleability  of  platinum,  which  can  be  easily  drawn  into  very  fine  wire; 
makes  the  alloy  harder;  more  difficult  to  fuse;  as  elastic  as  steel;  unchange- 
able in  the  air,  and  capable  of  taking  a  high  polish. 

While  platinum  is  but  little  cheaper  than  gold,  the  above  properties 
have  led  to  its  being  investigated  as  an  alloying  material  for  iron,  but 
as  yet  the  experiments  have  been  very  few,  and  limited  in  their  scope. 
Platinum  has  no  transformation  points,  and  it  consequently  reduces 
those  of  iron  when  mixed  with  it.  Up  to  10%  of  platinum,  two  transforma- 
tion or  recalescent  points  occur,  while  with  the  platinum  from  10  to  40% 
but  one  point  is  produced.  The  melting-point  diagram  shows  consider- 
able analogy  to  that  of  the  nickel-iron  alloys,  but  this  is  stronger  when 
the  alloys  are  rich  in  iron  than  when  they  are  rich  in  nickel  or  platinum. 

The  hardness  of  the  platinum  alloys  decreases  from  0  to  5%  of  platinum, 
and  then  gradually  increases  from  there  to  a  platinum  content  of  40%, 
after  which  it  remains  fairly  constant  until  90%  of  platinum  is  reached,  after 
which  it  declines  again.  At  50%  of  platinum  the  greatest  brittleness  occurs. 

From  0  to  90%  of  platinum  all  the  alloys  are  magnetic,  and  this  dimin- 
ishes in  the  same  ratio  as  the  iron  in  percentages  of  from  80  to  20  of  that 
metal.  Alloys  with  the  platinum  from  10  to  50%  lose  their  magnetic 
power  when  heated  to  from  1475°  to  1200°  F.,  and  it  returns  at  a  much 
lower  temperature  when  cooling.  Alloys  with  the  platinum  from  60  to 
90%  regain  their  magnetic  power  at  a  temperature  even  lower  than  this. 


INGREDIENTS   OF    AND    MATERIALS   USED   IN    STEEL  95 


NICKEL 

The  chemical  sub-group  in  which  nickel  belongs  is  composed  of  iron, 
cobalt,  and  nickel,  and  in  many  respects  they  are  very  similar.  It  occurs 
native  in  meteorites,  and  the  iron  meteorites  always  contain  nickel.  The 
principal  minerals  that  contain  it  are  nickeliferous  pyrites  and  garnier- 
ite.  Large  deposits  of  minerals  containing  both  nickel  and  copper  have 
been  found.  The  metals  are  reduced  together  and  put  on  the  market 
under  the  name  of  monel  metal. 

Nickel,  however,  is  separated  in  the  pure  form  for  many  uses,  and 
one  of  the  most  important  of  these  is  as  an  alloying  material  in  the  man- 
ufacture of  special  steels.  It  is  a  white  metal  with  a  slight  yellow  cast, 
and  is  very  hard  and  capable  of  being  highly  polished.  It  is  very  brittle 
in  its  ordinary  condition,  but  when  deoxidized  by  magnesium  becomes 
very  malleable. 

Nickel  reduces  the  size  of  the  crystalline  structure  and  increases  the 
toughness  of  steel.  It  brings  the  elastic  limit  closer  to  the  tensile  strength, 
and  microscopic  cracks,  that  are  liable  to  develop  into  larger  cracks  and 
produce  rupture,  do  not  appear  as  quickly  in  steels  containing  nickel 
as  those  without  it.  In  certain  proportions  it  also  makes  steel  more 
resilient  or  springy,  increases  the  hardness,  raises  the  tensile  strength,  and 
segregates  only  slightly. 

Nickel  was  first  added  to  steel  for  the  purpose  of  overcoming  the 
property  of  "sudden  rupture,"  which  is  inherent  in  all  carbon  steels. 
This  it  does  to  a  large  extent,  making  steel  better  able  to  withstand  severe 
shock  and  torsional  stresses,  as  well  as  compressive  stresses.  This  is  not 
due  to  hardening,  as  soft  steel  cannot  be  made  hard  by  the  addition  of 
nickel,  except  in  large  quantities,  and  it  is  considered  that  17.55%  of 
nickel  is  the  equivalent  of  only  1%  of  carbon. 

The  properties  of  nickel  steel  depend  as  much  upon  the  carbon  content 
as  on  the  nickel.  The  fact  that  a  2  or  3.5%  nickel  steel  is  used  means 
nothing  unless  the  carbon  content  is  right  for  the  use  to  which  the  steel 
is  to  be  put.  To  illustrate,  a  steel  containing  2%  nickel  and  0.12%  car- 
bon has  a  good  tensile  strength  with  a  great  elongation,  and  is  useful  for 
some  purposes,  while  a  steel  that  is  equally  useful  for  another  purpose 
may  contain  2%  nickel  and  0.9%  carbon,  and  this  would  give  it  a  high 
tensile  strength  with  very  little  elongation.  With  a  high  carbon  content 
nickel  steel  is  difficult  to  harden,  especially  locally,  as  fissures  and  cracks 
tend  to  develop  in  quenching.  It  also  has  more  tendency  to  warp  in 
quenching  than  other  steels  and  may  be  decarbonized  by  heating.  These 
tendencies  may  be  overcome  to  a  great  extent  if  the  metal  is  thoroughly 


96 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


annealed  before  it  is  machined  to  size,  in  order  to  relieve  all  of  the  internal 
strains.  Then,  when  quenched,  the  piece  should  be  immersed  in  the  bath 
so  that  the  liquid  can  cover  the  greatest  possible  surface  at  the  instant 
it  strikes  the  bath,  and  it  should  be  agitated  while  cooling. 


FIG.  47.  —  Cutting  test  bars. 

Nickel  also  gives  steel  a  tendency  to  show  laminations,  and  makes  it 
weaker  at  right  angles  to,  than  in  line  with,  the  direction  in  which  it  is 
rolled.  The  higher  the  nickel  content  the  greater  will  be  the  contrast 
between  the  strength  in  these  two  directions.  This  is  best  shown  by 


40          50 

Percentage  of  Nickel 

FIG.  48.  —  Effect  of  nickel  in  different  percentages. 

tests  which  were  made  on  test  bars  1  and  2,  cut  from  a  piece  of  3.5% 
nickel  steel  as  indicated  in  Fig.  47.  Test  bar  1  showed  an  elongation 
of  12%  and  a  reduction  of  area  of  17%.  Test  bar  2  gave  an  elongation 
of  25%  and  a  reduction  of  area  of  65%.  The  good  qualities  which  nickel 


INGREDIENTS    OF    AND    MATERIALS    USED    IN    STEEL  97 

gives  to  steel  offset  these  bad  qualities  to  such  an  extent  that  it  makes  a 
much  better  steel  for  gears,  crank-shafts  and  pieces  which  have  similar 
work  to  perform  than  the  ordinary  carbon  steel. 

Nickel  greatly  reduces  the  tendency  of  steel  to  be  damaged  by  over- 
heating, and  also  increases  the  effect  of  hardening  in  raising  the  strength 
of  the  metal.  One  series  of  tests  which  were  made  showed  a  tensile 
strength  of  88,000  pounds  per  square  inch,  an  elastic  limit  of  60,000 
pounds  per  square  inch,  an  elongation  of  28%  and  a  reduction  of  area 
of  58%  when  in  the  annealed  state.  These  figures  were  changed  by 
hardening  to  a  tensile  strength  of  225,000  pounds,  an  elastic  limit  of 
224,500  pounds,  an  elongation  of  8%,  and  a  reduction  of  area  of  19%. 
A  good  quality  of  carbon  steel  might  give  the  same  results  in  the 
annealed  state,  but  they  could  not  be  increased  to  nearly  the  same 
extent  by  means  of  the  ordinary  hardening. 

Nickel  has  one  peculiarity  in  its  influence  on  steel  which  is  best  shown 
by  Fig.  48.  It  increases  tensile  strength  and  elastic  limit,  but  steels 
containing  8  to  15%  of  nickel  are  so  brittle  that  they  can  be  powdered 
under  a  hand-hammer;  at  15%  of  nickel  the  toughness  begins  to  be 
restored;  from  20  to  25%  the  elongation  rapidly  increases,  and  from  there 
on  to  50%  a  gradual  increase  is  shown. 

Steel  with  percentages  of  nickel  from  30  to  35  gives  good  results  for 
valves  on  internal-combustion  engines,  as  the  nickel  makes  the  steel  wear 
better  and  it  is  not  as  good  a  conductor  of  "heat  as  other  metals.  Nickel 
steel  can  be  purchased  in  the  open  market  in  nearly  all  percentages  of 
nickel  from  1  up  to  35%,  and  with  varying  percentages  of  carbon. 

In  Fig.  49  is  shown  the  actual  results  that  were  obtained  from  a  series 
of  twenty  tests,  in  which  the  nickel  varied  from  0  to  20%,  and  the  other 
ingredients  remained  fairly  constant.  Ten  of  the  tests  were  with  forged 
steel  and  ten  with  cast  steel.  They  give  a  good  idea  of  the  strengths  that 
can  be  expected  in  nickel  steels,  although,  as  has  been  said  many  times, 
nickel  steel  in  the  annealed  or  natural  state  is  but  little  better  than  carbon 
steel,  but  if  properly  heat-treated  it  will  greatly  exceed  carbon  steel  for 
static  and  dynamic  strengths,  wearing  qualities,  etc. 

COBALT 

The  principal  minerals  containing  cobalt  are  smaltite  and  cobaltite, 
and  in  each  of  these  iron  and  nickel  take  the  place  of  a  part  of  the  cobalt. 
It,  like  nickel,  forms  compounds  that  are  analogous  to  ferrous  compounds, 
and  also  a  few  that  are  analogous  to  ferric  compounds.  In  the  latter 
case,  its  power  is  greater  than  that  of  nickel.  Cobalt  is  harder  than  iron, 
melts  at  a  slightly  lower  temperature,  and  has  a  silver-white  color  with  a 
tinge  of  red. 


98  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

In  the  matter  of  cobalt-iron  alloys,  investigations  up  to  a  cobalt  per- 
centage of  60  have  been  made.  The  mechanical  properties  were  but 
little  modified  in  these,  but  the  breaking  strength  and  the  elastic  limit 
increase  slowly,  while  the  elongation  and  the  reduction  in  cross-section  are 

!»uaraoH  auiWAI  uj  sptrao  j  tpui 


o  t2  m 

qoui  axetiDs  .tad  suoi 
tiOTjo'BJjuoo  pins  uorji?3u<y[g  jo  aSB^uaoi9<i 


inversely  modified.  Notwithstanding  its  similarity  to  nickel  the  cobalt 
steels  so  far  examined  have  no  industrial  interest  and  do  not  present  any 
of  the  qualities  of  the  nickel  steels. 

In  general,  cobalt  in  steels  enters  into  solution  in  the  iron,  and  the 
carbon  exists  therein  —  at  least  in  the  range  of  the  experiments  made 


INGREDIENTS    OF   AND    MATERIALS   USED    IN    STEEL  99 

—  in  the  shape  of  iron  carbide.  The  mechanical  properties  of  these  steels 
do  not  seem  to  promise  any  industrial  application;  but  they  show  very 
clearly  the  marked  difference  between  tin,  titanium,  and  silicon  steels  on 
the  one  hand,  and  nickel  and  cobalt  steels  on  the  other. 

CHROMIUM 

Chromium,  tungsten,  molybdenum,  and  uranium  are  in  the  same 
chemical  group,  and  all  show  some  resemblance  to  the  elements  in  the 
sulphur  group.  Each  forms  a  trioxide  which  is  acid  in  character,  and  lower 
oxides  which  have  little  or  no  acid  character. 

Chromium  forms  three  series  of  compounds.  It  occurs  in  nature 
principally  in  the  mineral  chromite,  which  is  commonly  called  chrome 
iron  ore,  or  chromic  iron,  with  the  composition  FeCr2O4.  It  is  a  very  hard 
metal  and  can  be  highly  polished;  has  a  bright  metallic  luster,  and  is  diffi- 
cult to  fuse,  its  melting  point  being  nearly  that  of  pure  iron.  It  burns 
brilliantly  in  oxygen,  though  it  is  not  changed  by  exposure  to  the  air  at 
ordinary  temperatures.  In  steel  making  it  is  used  as  a  ferro-chromium, 
containing  69%  chromium  and  40%  iron,  which  is  made  in  an  electric 
furnace  from  chrome  iron  ore. 

Chromium  gives  to  steel  a  mineral  hardness,  and  refines  the  grain 
remarkably,  owing  to  its  tendency  to  prevent  the  development  of  the  crys- 
talline structure;  but  it  gives  no  self-hardening  properties,  although  it 
is  the  element  used  in  combination  with  tungsten  to  produce  the  quality 
of  "red-hardness"  in  high-speed  steels. 

Chromium  added  to  steel  in  percentages  up  to  5  increases  the  ten- 
sile strength  and  elastic  limit  of  hardened  steel.  In  the  annealed  state 
the  tensile  strength  is  raised  until  6.5%  is  reached  and  the  elastic  limit 
is  raised  up  to  3%,  and  this  does  not  lower  to  any  great  extent  until  9% 
is  reached.  After  these  percentages  are  passed  a  decided  reduction  takes 
place.  This  is  best  shown  in.  Fig.  50. 

Extreme  hardness  may  be  obtained  in  chromium  steels  as  the  chromium 
intensifies  the  sensitiveness  of  the  metal  to  quenching,  and  greatly  reduces 
the  liability  of  fracture  that  is  found  in  carbon  steels.  This  is  due  to 
the  chromium  making  the  critical  changes  of  steel  take  place  much  more 
slowly.  Chromium  steel  practically  shows  no  grain  or  fiber  and  possesses 
a  high  power  of  resistance  to  shocks.  This  has  made  it  almost  universally 
used  for  armor  plate. 

With  2%  of  chromium,  steel  is  very  difficult  to  cut  cold,  and  is  quite 
brittle;  with  higher  percentages  than  this  it  is  impossible  to  finish  it  with 
machine  tools  except  by  grinding.  When  chromium  is  combined  with 
nickel  or  vanadium,  it  makes  the  strongest,  toughest,  and  best  wearing 
steel  on  the  market,  and  it  can  be  machined  and  forged  much  more  easily 
than  when  chromium  alone  is  used.  Small  gears  can  be  made  with  these 
alloying  materials  added  to  steel,  that  if  properly  heat-treated  will  be 


100 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


so  tough  and  strong  as  to  make  it  almost  impossible  to  break  out  a  tooth, 
even  with  a  sledge  hammer. 

Some  of  the  best  grades  of  chrome-nickel  or  chrome-vanadium  steel 
contain  from  0.75  to  1.50%  of  chromium.  If  more  than  this  is  used  the 
metal  is  too  brittle  and  it  is  difficult  to  preserve  the  high  strengths  which 
are  given  by  the  lower  percentages.  The  carbon  content  is  also  kept 
comparatively  low,  as  a  percentage  of  0.45  of  carbon  makes  the  metal 
about  as  hard  as  can  be  cut  with  machine  tools,  even  when  thoroughly 
annealed.  Many  of  these  steels  contain  only  0.25%  of  carbon  as  the 
chromium  gives  the  metal  a  hardness  similar  to  that  given  by  carbon, 
but  one  which  makes  the  cohesion  of  the  molecules  greater.  This  makes 
the  metal  much  more  homogeneous,  and  gives  it  the  ability  to  resist  shock 
and  torsional  stresses.  Thus,  this  alloy  is  one  of  the  best  steels  for  crank- 
shafts of  internal-combustion  engines  or  other  parts  of  machinery  which 
have  to  withstand  similar  vibrational  stresses. 


0.39       0.41 


Percentage  of  Carbon 
0.77        0.86  0.71 


1.27 


FIG.  50.  —  Effect  of  chromium  on  tensile  strength  and  elastic  limit. 

The  nickel-chrome  steels  are  difficult  to  forge,  as  it  is  dangerous  to 
hammer  them  after  the  temperature  has  dropped  below  that  which  makes 
the  metal  a  bright  yellow.  It  must  be  heated  many  times  to  forge  pieces 
of  any  size  or  of  intricate  shapes.  The  chrome-vanadium  steels,  however, 
are  no  more  difficult  to  forge  or  machine  than  the  0.40%  carbon  steels. 
Chrome  steels  for  armor  plate  are  made  with  the  chromium  content  about 
2%,  while  as  high  as  6%  is  used  in  some  of  the  high-speed  steels  when  the 
tungsten  or  molybdenum  content  is  high. 


TUNGSTEN 


Tungsten  forms  a  large  variety  of  compounds,  two  of  which  are  with 
oxygen,  namely:  the  dioxide  (WO2)  and  the  trioxide  (WO3).  The  trioxide 
forms  salts  with  bases  analogous  to  the  molybdates.  It  occurs  in  nature 


INGREDIENTS  OF  AND   MATERIALS  USED   IN  STEEL  101 

as  tungstates,  the  principal  one  of  which  is  wolframite  (FeWO4).  an  iron 
salt  that  always  contains  some  manganese.  It  is  very  hard,  difficult  to 
fuse,  and  forms  lustrous  steel-colored  laminae  or  a  black  powder. 

The  tungsten  metal  has  recently  been  used  quite  extensively  for 
incandescent  lamp  filaments  but  was  extremely  brittle  and  hence 
hard  to  work.  This  brittleness  was  considered  an  inherent  property 
of  the  metal  that  could  not  be  overcome.  Recently,  however  (April, 
1910),  ductile  tungsten  has  been  produced  at  a  cost  that  is  not  prohibi- 
tive. This  promises  to  make  a  radical  change,  as  when  reduced  several 
times  in  drawing  it  into  fine  wire,  about  .001  inch  in  diameter,  a  tensile 
strength  of  610,000  pounds  per  square  inch  has  been  obtained.  This  is 
nearly  double  that  of  piano  wire,  the  strongest  metal  known. 

Tungsten  as  an  ingredient  of  steel  has  been  known  and  used  for  a  long 
time,  it  having  been  used  in  the  celebrated  Damascus  steel,  but  its  actual 
effect  was  not  known  until  Robert  Mushet,  after  much  experimenting, 
brought  out  the  famous  "  Mushet  steel."  This  caused  some  radical 
changes  in  treating  crucible  steels,  and  much  progress  and  improvement 
has  been  made  since  that  time. 

The  effect  of  tungsten  on  steel  is  to  increase  hardness,  but  it  does  this 
chiefly  through  its  action  on  the  carbon.  In  other  words,  it  intensifies  the 
hardening  power  of  the  carbon.  If  the  percentage  of  tungsten  is  high 
with  a  proportionately  high  manganese  content  the  steel  will  be  very 
hard  even  when  cooled  in  air,  and  thus  is  made  possible  "  air-hardening " 
tool  steel. 

As  the  principal  use  of  tungsten  is  in  high-speed  tool  steel,  and  as  a 
high  percentage  of  manganese  makes  steel  that  is  liable  to  fire-crack,  to 
be  brittle,  to  be  weak  in  the  body,  and  to  be  less  easily  forged  and 
annealed,  the  manganese  is  now  kept  low  and  chromium  is  used  in  its 
place.  The  tungsten-chromium  steels  when  hardened  retain  their  hard- 
ness when  heated  to  a  dull  red  by  the  friction  and  pressure  of  chips  in 
cutting.  This  has  led  to  the  term  "red-hardness"  as  applied  to  this 
class  of  steel,  and  it  is  this  property  which  has  increased  the  cutting 
speeds  of  tools. 

Tungsten  when  added  to  steel  does  not  make  it  any  more  self-harden- 
ing than  the  carbon  tool  steels  if  the  manganese  and  chromium  are 
low,  but  every  increase  up  to  19%  increases  the  red-hardness  if  chro- 
mium is  increased  proportionately.  Beyond  19%  of  tungsten,  the  red- 
hardness  is  decreased  no  matter  what  the  percentage  of  chromium 
may  be.  The  increase  in  red-hardness  is  about  50%,  with  an  increase 
in  tungsten  from  6  to  19%,  and  that  with  manganese  as  low  as  0.15%. 
With  the  chromium  in  the  proper  percentage  tungsten  will  make  steel 
self-hardening  in  all  percentages  over  0.85,  but  if  the  chromium  is  too 
high  proportionately  the  steel  is  liable  to  become  injured  by  overheating 


102  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

when  the  lower  percentages  of  tungsten  are  used,  but  when  the  higher 
percentages  of  tungsten  and  chromium  are  used,  the  metal  can  be  heated 
to  just  below  the  melting  point  and  then  quenched  without  injury.  In 
fact,  with  the  tungsten  at  18%  and  the  chromium  6%  the  best  results 
for  cutting  tools  are  obtained  when  hardening  at  this  high  temperature. 

The  carbon  content  of  these  steels  is  kept  low  as  compared  with  ordi- 
nary tool  steels,  or  the  air-hardening  steels  of  a  few  years  ago.  The  car- 
bon content  in  the  high-speed  steels  of  to-day  usually  varies  between 
0.65  and  0.80%,  whereas  it  was  used  in  varying  percentages  up  to  2.4 
in  the  older  air-hardening  steels.  This  latter  percentage  was  used  in 
Mushet  steel. 

The  quality  of  red-hardness  given  steel  by  the  tungsten-chromium 
ingredients  increased  the  cutting  speed  of  tools  about  45%  over  that  of 
the  older  air-hardening  steels,  when  cutting  hard  forgings  or  castings. 
Similarly  an  increase  of  about  90%  was  made  when  cutting  softer  metals. 
This  has  led  to  their  almost  universal  use  to  the  exclusion  of  Mushet 
steel,  which  but  a  few  years  ago  filled  50%  of  the  sales  of  tool  steel. 

Tungsten  either  in  combination  with  manganese  or  chromium  has 
greatly  lessened  the  skill  and  knowledge  required  in  heat-treating  tool 
steel.  To  get  the  proper  degree  of  red-hardness  in  the  best  grades  of 
high-speed  steel,  they  should  be  heated  nearly  to  its  melting  point,  which 
is  about  2500°  F.  If  this  temperature  were  reached  it  would  soften  the 
steel  so  that  the  point  of  the  tool  would  run.  This  would  not  harm  the 
cutting  qualities  as  it  would  not  lessen  the  red-hardness  given  the  metal 
by  the  tungsten  and  chromium.  If  a  greater  temperature  were  reached 
it  would  melt  the  steel,  so  it  can  easily  be  seen  when  the  melting  temper- 
ature is  reached.  On  'the  other  hand,  if  a  temperature  of  2300°  F.  is 
reached,  the  same  red-hardness  will  be  given  the  steel,  so  that  there  is  a 
range  of  about  200°  that  will  give  the  same  results  in  heat-treating. 

The  carbon  tool  steels,  however,  have  to  be  heated  to  a  few  degrees 
above  the  recalescent  point  and  then  quenched  to  obtain  the  greatest 
degree  of  hardness.  After  this  they  must  be  drawn  to  remove  the  brittle- 
ness  caused  by  the  high  temperature.  This  requires  a  great  deal  of  skill 
to  judge  the  correct  temperatures,  as  a  variation  of  25  degrees  will  make 
quite  a  difference  in  the  temper  and  consequently  in  the  cutting  and 
wearing  qualities. 

MOLYBDENUM 

Molybdenum,  like  tungsten,  forms  a  large  variety  of  compounds, 
among  which  are  four  oxygen  compounds  that  include  a  mon-,  bi-,  and 
tri-oxide.  It  occurs,  principally,  in  nature  as  molybdenite,  which  is  the 
sulphide,  MoS2,  and  as  wulfenite,  the  lead  molybdate  (PbMoO4;)  also 
less  frequently  as  the  trioxide  (MoO3). 


INGREDIENTS   OF    AND    MATERIALS    USED    IN    STEEL          103 

Molybdenum  is  often  used  in  high-speed  steels  in  place  of  tungsten, 
as  its  action  is  very  similar.  Where  2%  of  tungsten  is  used,  1%  of  molyb- 
denum will  give  the  same  results,  that  is,  one  molecule  of  molybdenum 
appears  to  have  the  same  effect  as  one  molecule  of  tungsten,  its  atomic 
weight  being  double  that  of  tungsten.  The  cost  of  molybdenum  is  so 
much  higher  than  that  of  tungsten  that  its  use  is  prohibitive,  unless  much 
better  results  can  be  obtained,  but  a  few  high-speed  steel  makers  consider 
this  to  be  the  case  and  are  using  it  to  replace  the  tungsten  or  else  in  com- 
bination with  this  element. 

Many  experiments  have  been  made  with  molybdenum  in  place  of 
tungsten,  and  molybdenum  combined  with  tungsten,  but  these  showed 
considerable  irregularity  as  compared  with  the  tungsten-chromium  steels. 
The  cause  of  these  irregularities  was  not  determined  definitely,  but  the 
molybdenum  tools  seemed  to  run  at  their  highest  cutting  speeds  when 
heat-treated  at  a  lower  temperature  than  the  tungsten  steels.  This  would 
indicate  that  the  heat-treating  would  require  more  skill  in  judging  the 
temperature,  as  it  is  very  difficult  to  judge  a  definite  temperature  by  the 
color  of  the  steel  after  it  has  passed  a  yellow. 

Molybdenum  also  has  a  tendency  to  make  the  steel  more  brittle,  and, 
therefore,  weaker  in  the  body,  as  well  as  giving  it  a  tendency  to  fire-crack, 
which  is  a  serious  defect  in  tool  steel. 

URANIUM,  which  also  belongs  to  this  same  chemical  group,  has  stronger 
basic  properties  than  either  tungsten  or  molybdenum,  and  differs  from 
chromium  in  that  its  trioxide  forms  salts  with  acids.  Uranium  occurs 
chiefly  in  nature,  in  the  mineral  pitchblende,  or  uraninite,  which  consists 
of  the  oxide  (U3O8),  and  this  is  heated  in  the  electric  furnace  with  char- 
coal to  isolate  the  metal.  It  has  the  color  of  nickel. 

Owing  to  the  fact  that  uranium  resembles  nickel  and  has  many  of 
the  characteristics  of  the  other  members  of  the  chemical  group  to  which 
it  belongs,  many  experiments  have  been  carried  out  to  see  if  it  could  not 
be  made  a  beneficial  ingredient  of  steel.  None  of  these  experiments, 
however,  have  shown  that  it  was  as  good  as  the  other  materials  used 
daily  in  the  composition  of  steel,  and  its  chemical  actions,  as  described 
above,  would  not  make  it  appear  that  anything  could  be  expected  of  this 
element  that  could  not  be  obtained  with  cheaper  materials,  while  some 
detrimental  effects  might  be  obtained. 

VANADIUM 

Vanadium  occurs  in  nature  in  the  form  of  vanadates  or  salts  of  vanadic 
acid  (H3VO4),  which  is  analogous  to  phosphoric  acid.  When  used  in  steel 
making  its  direct  action  is  of  minor  importance,  but  it  acts  as  a  power- 
ful physic,  cleansing  the  steel  from  dissolved  oxides.  It  gives  the  best 


104  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

results  in  the  quaternary  steels,  such  ,as  vanadium-chromium-manga- 
nese-carbon, vanadium-nickel-manganese-carbon,  and  vanadium-tung- 
sten-chromium-carbon. It  has  an  affinity  for  oxygen  and  oxidizes  out 
of  the  steel  whenever  it  comes  in  contact  with  this  element.  There- 
fore it  has  the  property  of  elusiveness  to  a  marked  degree,  and  has  to 
be  handled  carefully  by  the  steelmakers  in  order  to  keep  it  in  the  finished 
metal. 

Vanadium  renders  possible  the  natural  formation  of  the  sorbitic  struc- 
ture, which  makes  the  steel  better  able  to  withstand  wear  and  erosion  by 
adding  to  its  self-lubricating  properties.  It  retards  the  segregation  of  the 
carbides,  which  renders  steel  susceptible  of  great  improvements  by  heat- 
treating.  Vanadium  produces  soundness  mechanically  as  well  as  chemi- 
cally, and  toughens  the  steel  by  acting  as  a  physic  on  the  other  ingredients 
and  scavenging  out  the  oxides  and  occluded  gases;  by  so  doing  it  increases 
the  molecular  cohesion.  The  percentage  of  oxygen  in  the  steel,  however, 
should  be  reduced  to  a  minimum  by  other  materials,  before  adding  the 
vanadium,  to  take  care  of  what  cannot  otherwise  be  removed,  as  it  is  too 
expensive  a  material  to  use  as  a  deoxidizer. 

Vanadium  seems  to  lessen  to  a  marked  degree  those  mysterious  fail- 
ures of  steel  characterized  as  due  to  " fatigue,"  "sudden  rupture,"  etc., 
but  which  is  better  named  crystallization.  This  is  doubtless  caused  by 
the  fact  that  the  cohesive  force  which  binds  the  molecules  of  the  metal 
together  has  become  weakened  by  the  work  that  the  steel  has  been  called 
upon  to  perform,  and  instead  of  combining  one  with  the  other  they  form 
into  microscopic  crystals.  This  it  does  by  making  the  metal  much  bet- 
ter in  its  dynamic  qualities,  that  is,  resistance  to  repeated  stresses,  alter- 
nating stresses,  and  simple  repeated  or  alternating  impacts.  Vanadium 
removes  nitrogen,  which  is  very  detrimental  to  steel  even  in  infinitesimal 
quantities.  Its  also  toughens  the  constituent  called  pearlite  and,  when 
used  in  combination  with  chromium,  reduces  the  mineral  hardness  given 
to  steel  by  this  element,  so  that  it  can  be  machined  and  forged  as  easily 
as  an  ordinary  carbon  steel. 

.  Vanadium  has  made  great  strides  in  the  past  few  years  as  an  alloying 
element,  and  is  used  in  steel  castings,  cast  iron,  and  the  bronzes  and  brasses, 
as  well  as  in  steel  mill  products.  In  one  respect  it  is  similar  to  carbon 
in  that  very  small  percentages  give  the  desired  results.  It  is  used  in 
percentages  varying  from  0.16  to  0.18  fop  the  moving  parts  of  machinery 
and  springs,  while  for  case-hardening  steel,  0.12%  is  sufficient.  In  high- 
speed steels  it  has  given  good  results  in  from  0.28  to  2%.  If  used  in  too 
large  a  quantity,  that  is,  much  over  0.30%,  it  dynamically  poisons  the 
metal,  and  the  dynamic  qualities  for  which  vanadium  steels  are  noted 
are  rendered  no  better  than,  if  as  good  as,  the  ordinary  carbon  steels.  In 


INGREDIENTS  OF  AND  MATERIALS  USED   IN   STEEL  105 

high-speed  steel,  however,  the  cutting  qualities  are  considered  of  greater 
importance  than  the  dynamic  strengths,  and  the  best  high-speed  steels 
that  have  been  placed  on  the  market  contained  1%  of  vanadium.  These 
steels  increased  the  cutting  quality  of  tool  something  over  10%  when 
working  on  hard  steel  or  castings. 

While  the  cost  of  vanadium-chrome  steel  is  from  6  to  10  cents  per 
pound,  one  firm,  which  builds  gasolene  engines,  claims  that  it  is  no  more 
expensive  in  actual  practice  than  carbon  steel,  and  is  much  cheaper  than 
nickel  steel,  owing  to  the  ease  with  which  it  is  machined  and  forged,  the 
lighter  weight  of  the  parts,  owing  to  its  great  strength,  and  the  greater 
accuracy  obtainable,  owing  to  the  uniformity  of  the  metal. 

Vanadium  steel  is  used  largely  for  crank-shafts,  connecting  rods, 
piston  rods,  axles,  crank-pins,  gears,  gun  barrels,  springs,  locomotive 
side  frames,  or  other  parts  of  moving  machinery  that  are  submitted  to 
vibrational,  impact  or  torsional  strains  and  stresses. 

TITANIUM 

Titanium  belongs  to  the  same  chemical  group  as  silicon,  and  three 
other  elements  which  are  quite  rare.  In  some  respects  it  resembles 
carbon.  It  forms  a  compound  with  oxygen,  namely,  TiO2,  and  this  tita- 
nium dioxide  occurs  in  nature  in  three  distinct  forms.  The  principal 
one  of  these  is  the  titaniferous  ores  that  contain  ferrous  titanate 
(FeTi03). 

It  is  very  difficult  to  reduce  in  the  blast  furnace  and  thus  make 
beneficial  to  the  metal,  but  when  separated  in  the  electric  furnace 
and  made  into  a  ferro-titanium,  that  contains  from  12  to  15%  tita- 
nium, about  6%  of  carbon,  and  5%  of  all  other  impurities,  with  the 
balance  iron,  it  greatly  improves  steel  and  iron,  if  added  in  the  proper 
proportions. 

Titanium  burns  more  energetically  in  oxygen  than  any  known  sub- 
stance. When  heated  in  oxygen  it  creates  an  instantaneous  dazzling 
flame  like  lightning.  Its  combination  with  nitrogen  gas  is  attended 
with  the  evolution  of  heat;  it  being  the  only  undisputed  example  of 
the  combustion  of  an  element  in  nitrogen.  While  nickel,  chromium, 
molybdenum,  and  tungsten  add  certain  good  qualities  to  steel,  none  of 
these  combine  with  nitrogen  and  thus  remove  it  from  the  metal  as  tita- 
nium does. 

Titanium  has  a  great  affinity  for  nitrogen  and  carries  this  off  into 
the  slag;  nitrogen  being,  at  least,  as  detrimental  to  the  physical  proper- 
ties of  steel  as  phosphorus,  and  present  in  larger  percentages  than  has 
hitherto  been  supposed.  It  also  has  a  strong  affinity  for  and  removes 
oxygen.  By  removing  the  oxygen  and  nitrogen  it  prevents  the  injurious 


106  COMPOSITION    AND    HEAT-TREATMENT    OF   STEEL 

effects  of  these  elements  on  the  steel.  Titanium  forms  with  oxygen  an 
oxide  and  with  nitrogen  a  stable  nitride  that  shows  as  tiny  red  crystals 
under  the  microscope.  Both  of  these  substances  are  then  carried  off  into 
the  slag.  The  quantity  of  slag  that  is  removed  or  lifted  from  the  molten 
metal  is  also  increased.  Unless  an  unnecessary  quantity  of  the  alloy  is 
used,  the  titanium  itself  passes  off  with  the  slag,  and  will  not  show  on  the 
analysis  of  the  metal.  The  titanium  itself  is  of  no  special  benefit  as  a 
component  of  the  finished  steel,  and  only  enough  should  be  used  to  remove 
the  impurities.  Any  excess  above  this  will  remain  in  the  steel,  and  if 
proof  is  wanted  that  one  is  buying  a  titanium-treated  metal,  enough  of 
the  alloy  could  be  used  to  show  by  analysis,  as  a  small  percentage  left  in 
the  steel  is  not  harmful. 

One  instance  of  the  removal  of  nitrogen  was  shown  in  some  ordinary 
Bessemer  steel  rails  that  were  found  to  contain  from  .013  to  .015%  of 
nitrogen.  When  0.50%  of  ferro-titanium  containing  15%  of  titanium 
was  added,  the  nitrogen  was  reduced  to  from  0.004  to  0.005%.  As  it 
also  has  a  strong  affinity  for  oxygen  it  provides  a  simple  means  of  thor- 
oughly deoxidizing  steel. 

Titanium,  by  removing  the  oxygen  and  nitrogen,  prevents  the  forma- 
tion of  blow-holes  in  steel.  It  also  reduces  the  size  of  the  pipe,  as  it  makes 
the  bath  more  liquid  by  freeing  it  from  the  free  oxide  and  slag.  This 
makes  the  metal  subside  in  the  mold  while  cooling,  and  the  pipe  will 
be  smaller  and  flatter.  It  also  makes  it  roll  well.  In  this  connection  the 
record  of  a  day's  work  in  rolling,  as  taken  from  a  pyrometer,  showed  an 
increase  of  not  less  than  30°  F.  in  the  heat  of  the  metal  at  a  given  point. 
That  is,  30°  above  that  of  untreated  metal  at  the  same  point,  while  passing 
through  the  roll.  The  metal  almost  invariably  does  not  boil  but  lays 
dead  in  the  ingot  molds. 

Due  to  the  removal  of  nitrogen  and  oxygen  from  the  steel,  the  physical 
properties  are  improved  and  its  density  increased.  The  tensile  strength, 
elastic  limit,  reduction  of  area,  transverse  strength,  hardness,  elasticity, 
wearing  qualities,  resistance  to  shocks,  and  torsion,  are  greatly  improved. 
Thus  titanium  gives  practically  the  same  results  as  vanadium,  and  the 
ferro-titanium  can  be  produced  for  a  fraction  of  the  cost.  One  example 
of  its  ability  to  withstand  torsional  strains  was  shown  with  a  bar  4  feet 
long  and  If  inches  square.  This  was  twisted  through  seven  complete 
revolutions  without  the  sign  of  a  fracture.  The  Brinell  hardness  test 
shows  titanium  steel  to  be  softer  than  ordinary  steel  rails  of  the  same 
analysis  and  section,  and  this  is  probably  due  to  the  finely  divided  ferrite 
network. 

A  ferro-titanium  alloy  that  contains  from  10  to  15%  of  titanium 
gives  the  best  results,  as  this  goes  into  almost  instant  solution.  When 
a  higher  percentage  is  used  the  titanium  is  always  liable  to  segregate, 


INGREDIENTS  OF  AND  MATERIALS  USED  IN  STEEL  107 

as  it  has  a  much  higher  melting  point  than  that  of  steel.  Thus  when  a 
25%  alloy  was  tried  nothing  was  gained  by  its  use.  When,  however, 
an  alloy  is  used  that  will  allow  the  titanium  to  enter  into  solution  in  the 
molten  metal  it  retards  the  segregation  of  the  other  ingredients  and 
produces  a  very  homogenous  steel. 

One  per  cent  of  the  10  to  15%  ferro- titanium  alloy  is  all  that  is  neces- 
sary to  add  to  the  steel,  as  this  amount  will  seize  all  of  the  oxygen  and 
probably  all  of  the  nitrogen  that  has  been  left  in  the  bath.  In  many  cases 
this  can  be  reduced  to  one-half  of  1%,  and  after  some  experience  in  its 
use  the  one-half  of  1%  might  be  sufficient  for  all  steels.  This  small 
amount  removes  the  bulk  of  the  blow-holes  and  segregation  found  in 
Bessemer  steel,  and  in  the  case  of  steel  rails  it  only  increases  their  cost 
about  $2  per  ton.  With  the  titanium  steel  rails  numerous  use  tests  have 
been  made,  and  all  of  these  prove  that  they  wear  about  three  times  as 
long  as  the  ordinary  steel  rails,  while  in  some  cases  they  have  outworn 
six  of  the  Bessemer  rails. 

In  the  Bessemer  and  open-hearth  process  of  steel  making  it  is  always 
best  to  add  the  ferro-titanium  in  the  ladle.  It  should  be  shoveled  in 
loosely,  and  never  preheated  but  used  cold.  The  first  shovelful  should 
be  put  in  after  the  bottom  of  the  ladle  is  well  covered  with  molten  metal 
and  after  the  ferro-manganese  has  been  added.  One  shovelful  at  a  time 
should  then  be  thrown  in  while  the  ladle  is  filling,  so  as  to  give  it  the  bene- 
fit of  the  swirling  and  churning  motion  of  the  molten  mass.  The  last 
shovelful  should  be  added  before  the  ladle  is  three-quarters  full.  One 
reason  for  this  is  that  the  alloy  is  lighter  than  iron  and  would  not  sink 
and  disseminate  through  the  bath  if  it  were  added  near  the  top,,  Another 
reason  is  that  if  it  were  near  the  slag  it  would  unite  with  the  oxygen  in 
the  slag  and  consequently  would  not  benefit  the  metal. 

The  alloy  should  never  be  used  in  connection  writh  aluminum,  as  alumi- 
num adds  brittleness  and  titanium  removes  brittleness;  hence  the  two 
alloys  are  antagonistic,  and  the  titanium  will  do  its  work  much  better 
alone. 

In  crucible  steel  making  it  is  sometimes  preferable  to  add  the  titanium 
alloy  with  the  charge  of  metal  that  is  to  be  melted  down,  and  in  this  case 
it  should  be  added  well  down  toward  the  bottom  of  the  crucible.  It  has, 
however,  been  successfully  added  after  the  metal  is  melted,  and  when  the 
manganese  is  added.  At  this  time  the  titanium  alloy  should  be  added 
after  the  manganese.  In  fact,  at  all  times  it  should  be  the  last  material 
added  to  the  bath. 

After  adding  the  alloy  the  ladle  of  metal  should  be  held  for  from  5 
to  15  minutes  before  pouring  in  order  to  allow  the  titanium  to  do  its 
work  and  scavenge  out  the  oxygen  and  nitrogen.  There  is  little  danger  of 


108  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 

the  metal  in  the  ladle  becoming  chilled  by  holding  it,  as  the  reaction 
caused  by  titanium  tends  to  cause  its  temperature  to  rise  rather  than 
lower,  and  the  metal  is  in  better  condition  for  pouring  after  standing 
than  before.  In  one  case  a  ladle  of  steel  was  held  for  20  minutes  after 
tapping  and  adding  the  titanium,  and  is  said  to  have  then  been  in  better 
condition  for  pouring  into  ingots  than  is  steel  without  titanium  soon  after 
it  is  tapped. 

Titanium  also  prevents  steel  from  heating  up  as  quickly  as  steels 
in  which  it  is  not  used.  An  instance  of  this  was  some  titanium-treated 
ingot  molds  that  did  not  show  red  in  the  dark  when  filled  with  molten 
steel,  whereas,  the  ordinary  ingot  molds,  standing  beside  them,  were 
distinctly  red  hot.  The  metal  is  also  comparatively  slow  in  heating  from 
friction,  and  this  is  one  of  the  causes  why  metals  treated  with  it  are  much 
more  durable  than  others.  Steels  treated  with  titanium  heat  up  more 
slowly  than  others  when  machining  them.  The  cutting  speed  can  there- 
fore be  increased,  and  the  machine  work  done  more  quickly.  This  also 
makes  it  very  advantageous  to  use  in  tool  steels;  whether  of  the  carbon 
or  high-speed  kind. 

Owing  to  the  fact  that  titanium  increases  the  heat  of  the  molten  metal 
to  a  very  marked  degree,  it  is  seldom  necessary  to  use  much  ferro-silicon, 
as  silicon  is  largely  used  for  this  purpose.  Silicon,  however,  is  not  so 
efficacious  and  is  known,  at  times,  to  precipitate  phosphorus  with  disas- 
trous results.  Thus,  when  titanium  is  used  the  proportion  of  ferro-silicon 
should  be  decreased  and,  if  possible,  eliminated  entirely.  If  not  eliminated 
entirely,  it  could  be  reduced  from  time  to  time  until  no  further  improve- 
ment is  noticed.  If  defects  are  found  in  the  surface  of  the  finished  steel, 
a  slight  increase  in  the  ferro-manganese  and  a  decided  decrease  in  the 
ferro-silicon  used  will  overcome  that. 

Steel  castings  that  have  been  treated  with  titanium  are  more  blue  in 
color,  free  from  blow-holes  and  brittleness,  and  heat  less  under  cutting 
tools  than  ordinary  steel  castings;  thus  they  can  be  machined  more  easily 
and  rapidly.  The  transverse  strength  has  been  increased  from  17  to 
23%  by  its  use. 

Titanium  increases  the  breaking  strains,  wearing  qualities,  and  hard- 
ness in  the  chill  of  cast  iron,  and  hence  is  very  beneficial  for  such  castings 
as  car-wheels,  but  it  decreases  the  chilling  effect. 

Titanium  also  promises  some  good  results  when  used  in  copper,  brass, 
or  bronze,  in  which  case  a  cupro-titanium  instead  of  a  ferro-titanium  is 
used.  This  has  been  used  in  about  the  same  proportions  as  the  ferro, 
but  the  best  results  have  been  obtained  in  copper  with  from  li  to  2% 
of  the  cupro-titanium. 


INGREDIENTS   OF    AND    MATERIALS    USED    IN    STEEL 


109 


ALUMINUM 

Aluminum  is  the  third  element  in  the  earth's  crust  in  importance,  and 
comprises  7.81%  of  it.  It  occurs  widely  distributed  and  in  many  forms  of 
combination;  one  of  the  most  common  of  which  is  clay,  where  it  exists 
in  various  conditions  of  purity.  It  is  only  within  recent  years,  however, 
that  it  could  be  separated  from  its  impurities  cheaply  enough  to  make  it 
a  commercial  metal. 

Since  aluminum  has  come  into  prominence  in  metallurgy  it  has  found 
many  uses,  and  one  of  these  is  in  the  making  of  steel.  This  element, 
however,  is  only  used  as  a  purifier,  as  it  adds  nothing  to  the  strength  of 
steel  except  in  so  far  as  it  removes  some  of  the  impurities. 

Aluminum  suppresses  the  evolution  of  gas  either  by  increasing  the 
metal's  solvent  power  for  that  gas  or  by  removing  the  oxygen,  and  thus 


0.15 


0.20 


Percentage  of  Carbon 
0.25 


234 
Percentage  of  Aluminum 


FIG.  51.  —  Effect  of  aluminum  on  steel. 

preventing  the  later  formation  of  carbonic  oxide,  or  by  both  means  jointly. 
This  makes  the  metal  more  dense  by  removing  the  microscopic  bubbles 
formed,  and  greatly  decreases  the  tendency  to  segregation,  as  the  alu- 
minum has  a  quieting  effect  on  the  molten  metal. 

Only  enough  aluminum  is  used  to  cause  this  effect,  and  thereafter 
work  out  of  the  metal.  If  the  solid  alumina  produced  remains  suspended 
in  the  metal  it  causes  a  lack  of  continuity  of  the  metallic  structure,  and 
thus  a  loss  of  strength. 

Fig.  51  shows  the  effect  of  aluminum  on  the  tensile  strength,  elastic 
limit,  and  elongation  of  steel  with  various  percentages  of  carbon. 


OTHER   ALLOYING    ELEMENTS 

Some  tin  steels  have  been  made.  These  cannot  be  rolled.  If  there 
be  more  than  1%  of  tin  present  they  are  extremely  hard  and  brittle. 
Annealing  has  the  same  effect  upon  these  as  upon  the  ordinary  steels 
and  there  is  in  no  case  precipitation  of  the  carbon  in  the  state  of  graphite. 


110  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

Yttrium  has  been  mentioned  as  an  alloying  element  for  steel,  but  it 
is  only  found  in  combination  with  a  few  rare  minerals,  and  consequently 
is  only  seen  in  the  laboratory.  It  belongs  to  the  same  chemical  group 
as  aluminum,  and  if  it  were  found  to  be  beneficial  to  steel  it  could  not  be 
obtained  in  sufficient  quantities  for  commercial  use. 

Cerium  and  lanthanum  have  been  combined  with  iron  in  the  electric 
furnace  to  make  an  alloy  that  will  give  off  luminous  sparks.  The  maxi- 
mum sparking  effect  seems  to  be  obtained  with  about  50%  of  iron,  and 
this  will  light  illuminating  gas.  The  sparks  are  obtained  by  striking  the 
alloy  with  steel  similar  to  the  way  flint  was  used  before  the  days  of  matches. 
Some  such  combination  might  be  used  for  generating  the  spark  in  internal- 
combustion  engines.  One  such  alloy  was  sold  to  the  match  trust  and 
killed,  as  they  feared  competition  from  its  use. 


CHAPTER  VII 

WORKING  STEEL  INTO  SHAPE 

Rolling 

AFTER  the  iron  ore  has  been  reduced  to  pig  metal,  and  this  refined  and 
combined  with  the  other  ingredients  that  go  into  the  making  of  the  dif- 
ferent grades  of  steel,  and  then  cast  into  ingots,  the  ingots  are  sent  through 
slabbing  rolls,  as  shown  in  Figs.  52  and  53.  The  slabs  thus  formed  are 
then  rolled  into  the  numerous  shapes  that  are  used  for  manufacturing 
purposes. 

The  slabbing  mill,  with  a  single  pair  of  rolls  and  stationary  table, 
which  is  used  by  many  steel  makers,  is  shown  in  Fig.  52.  In  Fig.  16  is 
shown  the  mechanically  operated  grip  that  has  just  brought  an  ingot  from 
the  soaking  pit,  and  dropped  it  onto  the  carrier  that  conveys  it  to  the  rolls, 
and  Fig.  17  shows  the  same  ingot  just  as  it  has  made  its  first  pass  through 
the  slabbing  mill.  After  this  the  mill  is  reversed  and  the  ingot  passes 
back  through  another  section  of  the  rolls  to  further  reduce  it.  After 
some  four  or  five  passes  back  and  forth  through  the  rolls,  during  which 
time  it  is  turned  over  so  as  to  roll  all  four  sides,  it  is  sent  to  other  rolls 
that  reduce  it  to  commercial  shapes. 

In  Fig.  53  is  shown  the  three  high  mill  with  tilting  table.  This  has  a 
double  set  of  rolls,  and  for  the  first  pass  of  the  ingot  the  end  of  the  table 
next  to  the  rolls  is  lowered  to  receive  it  as  it  comes  through.  The  rollers 
of  the  table  are  then  reversed,  and  while  reversing  the  end  of  the  table  is 
elevated,  as  shown  in  the  illustration,  and  the  ingot  sent  back  through 
the  upper  rolls.  The  rolls,  as  well  as  the  tilting  table,  are  controlled 
from  the  platform  of  the  pulpit,  shown  to  the  right  of  the  picture.  In 
this  design  a  much  narrower  mill  can  be  used  for  the  same  number  of 
passes  than  in  the  design  of  mill  shown  in  Fig.  52. 

After  slabbing  the  metal,  various  kinds  of  rolling  mills  are  used  to  get 
the  steel  into  the  shapes  desired.  Many  times  the  different  mills  are 
combined  so  as  to  make  the  rolling  operations  continuous  from  the  steel 
furnace  to  the  finished  product.  In  some  cases  the  desired  shape  is  fin- 
ished before  the  metal  has  had  time  to  cool  off  after  leaving  the  fur- 
Ill 


112  COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


WORKING  STEEL  INTO  SHAPE 


113 


114 


COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 


nace  in  which  it  was  refined.  In  Fig.  54  is  shown  the  metal  being  reduced 
to  rods  in  a  wire  mill,  and  the  kind  of  rolls  used.  Here  the  rods  run  into 
a  track  as  they  leave  the  rolls,  and  this  guides  them  to  the  next  roll  that 
further  reduces  the  metal  in  size. 

CRYSTALLINE    STRUCTURE    OF   METAL 

Steel  that  has  cooled  slowly  from  the  liquid  state,  as  is  the  case  with 
that  which  has  been  cast  into  ingots  from  the  converter,  furnace,  or  cru- 
cible, forms  into  crystals  which  do  not  show  the  same  structure  throughout. 


FIG.  54.  —  Rod  mill  with  track  and  water-cooled  rolls. 

The  outer  shell  of  the  ingot  will  have  a  different  structure  from  the  rest 
of  the  mass  due  to  its  cooling  quickly,  and  therefore  it  is  under  strains 
until  the  center  of  the  ingot  has  cooled.  The  top  of  the  ingot  also  has 
an  area  of  abnormal  crystallization  which  is  due  to  segregation.  There 
is,  however,  the  same  general  crystalline  character  in  the  largest  part 
of  the  ingot. 

In  passing  the  steel  between  rolls,  to  reduce  it  to  the  sizes  and  shapes 
wanted  in  the  finished  material,  this  crystalline  grain  is  broken  up  and  a 
new  grain  which  is  much  finer  takes  its  place.  The  best  results  are  ob- 
tained if  the  rolling  is  completed  at  a  temperature  just  above  its  highest 
point  of  transformation,  as  at  or  just  above  this  point  a  new  grain  struc- 
ture is  born  which  makes  the  metal  more  homogeneous. 

This  formation  of  grain  continues  after  the  steel  leaves  the  rolls  and  until 


WORKING    STEEL    INTO    SHAPE  115 

it  has  cooled  below  its  lowest  point  of  transformation,  below  which  point 
no  more  change  will  take  place. 

In  rolling  steel  it  is  frequently  heated  to  from  2000°  to  2400°  F.,  and 
it  would  seem  that  this  would  seriously  damage  it.  This  would  be  so 
if  it  were  not  for  the  fact  that  the  mechanical  pressure  exerted  upon  the 
metal  by  the  rolls  breaks  down  the  large  crystals  formed  by  this  high 
temperature,  and  reduces  them  to  a  small  size.  The  final  size  of  the  crys- 
tals is,  therefore,  dependent  upon  the  temperature  of  the  steel  at  the 
finish  of  the  rolling  process. 

Finished  steel  has  a  finer  grain  structure  if  the  last  rolling  operation 
receives  the  metal  at  a  temperature  which  is  falling  from  1650°  F.  to 
1400°,  which  are  the  highest  and  lowest  points  of  transformation,  than 
if  it  was  finished  at  2000°  F.,  or  any  temperature  above  the  highest  point 
of  transformation.  On  the  other  hand,  if  the  rolling  be  continued  after 
the  temperature  of  the  steel  has  fallen  below  the  lowest  point  of  trans- 
formation, strains  are  set  up  which  make  the  piece  unfit  for  most  uses 
until  it  has  been  thoroughly  annealed. 

RULES   FOR   ROLLING 

Four  rules  might  be  established  in  rolling  steels  which  will  affect  the 
final  size  of  the  grain  so  as  to  make  it  what  it  should  be,  and  these  are: 

First. — The  rolling  operations  should  be  continuous  from  the  highest 
temperature  employed  down  to  the  finishing  temperatures,  as  long  waits, 
such  as  are  generally  made  necessary  when  the  metal  is  formed  roughly 
to  shape  and  size  at  a  high  heat,  then  allowed  to  cool  and  a  little  work 
done  upon  it  at  the  lower  temperature,  are  liable  to  cause  a  coarse  grain 
that  cannot  be  made  fine  by  the  last  rolling. 

Second.  —  There  are  better  results  obtained  if  the  steel  is  passed 
several  times  through  the  rolls  with  a  small  reduction  in  the  size  of  the 
metal  each  time,  than  if  a  large  reduction  is  made  with  a  very  few  passes. 

Third. — In  rolling  a  large  piece  a  great  reduction  can  be  made  during 
the  first  pass  through  the  rolls,  and  the  amount  of  reduction  gradually 
decreased  with  each  passage  through  the  rolls  until  the  finishing  roll 
gives  it  just  the  right  amount  of  reduction  conducive  to  the  making  of 
the  grain  as  fine  as  the  steel  will  assume. 

Fourth.  —  The  steel  should  reach  the  finishing  roll  so  that  the  tem- 
perature will  be  falling  from  1650°  F.  to  1400°  while  it  is  passing  through 
the  rolls.  It  should  not  be  allowed  to  go  below  1300°  until  all  the  rolling 
operations  have  been  finished. 


116  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

HIGH   AND   LOW   TEMPERATURES 

Steel  is  so  mobile  at  very  high  temperatures  that  it  yields  to  distortion 
by  the  crystals  sliding  past  one  another,  but  as  the  temperature  decreases 
the  mobility  of  the  mass  becomes  less,  and  less  sliding  is  possible.  The 
crystals  then  crush  against  each  other,  and  at  the  lower  temperatures  a 
crushing  of  the  crystals  only  takes  place. 

To  obtain  the  very  best  qualities  in  a  0.50%  carbon  steel  that  it  is 
possible  to  produce,  the  work  of  rolling  should  be  completed  just  at 
the  time  when  the  ferrite  is  separating  from  solid  solution.  Rolling 
the  work  below  the  temperature  at  which  this  occurs,  which  is  while  the 
metal  is  cooling  from  1650°  F.  to  about  1300°,  greatly  increases  the  brittle- 
ness  of  the  metal.  Rolling  the  steel  at  a  higher  temperature  lowers 
the  strength,  owing  to  the  coarser  grain  which  is  given  the  metal.  For 
steels  of  all  other  carbon  contents  it  is  logical  to  assume  that  the  same 
rules  hold  good,  but  it  is  possible,  although  not  probable,  that  further 
investigations  may  change  them. 

Steels  are  rolled  in  a  large  variety  of  standard  shapes,  such  as  round, 
square,  oblong,  hexagon,  octagon,  tubes,  and  L,  T,  U,  I  shapes,  etc.,  and 
can  be  obtained  in  nearly  any  special  shape  desired,  providing  enough 
is  wanted  to  pay  for  the  making  of  rolls. 


Casting 

APPARATUS    FOR    MELTING 

Casting  steel  consists  of  pouring  the  metal  in  a  fluid  state  into  molds 
which  give  it  the  desired  shape.  These  shapes  can  be  given  most  any 
kind  of  an  intricate  form  owing  to  the  shape  being  given  the  mold  by  a 
pattern  and  cores. 

Many  different  methods  are  used  for  melting  the  steel,  and  some  of 
these  are  the  same  in  principle  as  those  used  for  converting  the  blast- 
furnace metal  into  steel. 

Pig  iron  and  steel  are  melted  together  in  the  cupola,  but  this  is  not 
a  normal  product.  It  is  a  hybrid  metal  sometimes  called  semi-steel  which 
is  useful  for  special  purposes,  but  fundamentally  different  from  any  kind 
of  steel.  It  is  a  little  better  than  cast  iron,  and  is  a  very  cheap  mixture 
comparatively. 

The  open-hearth  furnace  is  used  a  great  deal  for  melting  steel,  for 
steel  castings,  and  might  be  considered  the  cheapest  method  of  turning 
legitimate  steel  into  castings.  Scrap  steel  and  iron  are  used  in  this  fur- 
nace, but  they  are  melted  under  an  oxidizing  flame,  and  the  metalloids 


WORKING    STEEL    INTO    SHAPE  117 

are  almost  entirely  eliminated,  thus  giving  a  definite  starting  point  from 
which  a  known  and  regular  metal  can  be  made  by  the  addition  of  recar- 
burizers.  Both  the  acid  and  basic  open-hearth  processes  are  used  for 
steel  castings. 

The  Bessemer  converter  in  small  sizes,  often  known  as  "the  baby  Bes- 
semers,"  is  extensively  used  for  making  steel  for  castings.  There  are  many 
modifications  of  these  small  converters,  such  as  the  Tropenas  converter, 
the  Stoughton  or  long  tuyere  converter,  and  others.  The  Tropenas  con- 
verter process  is  largely  used  when  making  steel  castings,  and  this  if 
properly  run  gives  good  results  in  the  castings.  In  the  Bessemer  con- 
verter the  blast  is  blown  in  at  the  bottom,  while  in  the  Tropenas  process 
the  air  is  blown  at  a  low  pressure  upon  the  surface  of  the  molten  metal. 
Some  four  to  seven  inches  above  this  set  of  tuyeres  is  another  set,  which 
supplies  air  to  burn  the  carbonic  oxide,  the  upper  set  not  being  operated 
until  the  blowing  is  well  under  way. 

The  crucible  process  has  been  used  to  some  extent  for  small  castings, 
and  to  cast  some  of  the  special  alloyed  steels.  Its  condition  of  "dead- 
melt"  %ives  a  more  quiet  metal,  generates  less  gas  when  the  metal  comes 
in  contact  with  cold  surfaces,  and  the  castings  are  more  apt  to  be  free 
from  blow-holes;  in  fact,  a  German  foundry,  by  using  special  care  in  the 
mixing  of  the  metal,  melting  it,  and  making  the  molds,  guarantees  castings 
free  from  blow-holes,  and  makes  castings  of  any  composition  of  metal 
from  wrought  iron  to  high-carbon  or  high-speed  steels. 

This  method  produces  the  best  steel  castings,  but  it  is  the  most  expen- 
sive way  of  making  them. 

The  electric  furnace  is  just  beginning  to  be  used  for  melting  the  metal 
for  steel  castings,  but  it  promises  very  good  results  as  the  phosphorus 
and  sulphur  can  be  reduced  to  a  trace,  and  the  oxygen  and  nitrogen  can 
be  very  materially  reduced. 


RISERS,    GATES,    ETC. 

In  making  steel  castings  about  40%  of  the  melt  is  used  to  supply 
risers,  sprues,  gates,  etc.,  and  there  is  consequently  a  loss  in  remelting 
these. 

The  risers,  which  are  sometimes  called  sink-heads,  run  from  the 
top  of  the  mold  to  the  casting  and  are  put  on  all  thick  sections  of  the 
casting  to  feed  the  metal  to  it  while  it  is  cooling  and  shrinking.  These 
must  be  kept  from  solidifying  until  after  the  casting  has  become 
solid. 

The  sprue  is  the  name  given  the  opening  into  which  the  metal  is 
poured,  and  this  runs  from  a  basin  in  the  top  of  the  mold  to  a  pocket, 


118 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


which  is  usually  located  near  the  bottom  of  the  casting.  From  this  lower 
pocket  to  the  opening  in  the  mold,  which  is  to  form  the  casting,  are  cut 
other  openings  so  the  metal  will  be  able  to  flow  in.  These  openings  are 
called  gates.  This  arrangement  is  made  necessary  to  prevent  the  liquid 
metal  from  tearing  up  the  mold,  as  it  would  do  if  poured  directly  into 
the  opening  that  forms  the  casting.  The  metal  left  in  these  when  the 
casting  is  poured  has  to  be  broken  away  from  and  chipped  and  sawed  off 
of  the  casting.  They  are  then  remelted  to  make  other  castings. 


COMPOSITION    OF   STEEL   CASTINGS 

Steels  with  various  alloying  materials  and  of  numerous  different  com- 
positions are  being  used  for  castings  to-day.  The  carbon  content  of 
these  varies  with  the  use  to  which  the  casting  is  to  be  put.  Over  0.70% 
carbon  is  seldom  used  in  castings,  owing  to  its  making  the  steel  too  hard 
to  machine,  and  in  complicated  shapes  the  shrinkage  cracks  are  liable 
to  become  dangerous. 

In  the  ordinary  steel  castings  manganese  should  not  exceed- 0.70% 
for  soft  castings  and  0.80%  for  hard  ones,  as  more  than  this  is  liable  to 
make  the  metal  crack  when  shocks  are  applied  to  it.  Silicon  may  have 
a  percentage  of  0.10  in  the  soft  castings,  and  0.35%  in  hard  ones  without 
diminishing  the  toughness.  Aluminum  is  used  by  many  in  making  cast- 
ings, as  it  has  a  great  affinity  for  oxygen,  and  will  remove  the  last  trace 
of  this  from  the  iron.  It  also  aids  in  dissolving  the  gases.  It  has  a  ten- 
dency to  make  the  metal  sluggish,  but  it  enables  it  the  better  to  run  through 
small  passages  as  without  it  the  metal  foams  and  froths  when  it  comes 
in  contact  with  cold  surfaces,  thus  impeding  the  flow  and  chilling  the 
advance  guard  of  the  stream.  Aluminum  should  oxidize  out  of  the  steel, 
and  not  show  over  0.20%  when  the  steel  is  analyzed,  but  it  is  better  if 
only  traces  are  left,  as  it  decreases  the  ductility. 

Sometimes  the  phosphorus  is  allowed  to  be  as  high  as  0.08%,  but  when 
the  castings  are  to  be  submitted  to  physical  test  the  phosphorus  and  sul- 
phur should  be  kept  below  0.05%. 

The  physical  properties  of  ordinary  steel  castings  should  be  above 
the  figures  in  the  following  table: 


Hard 
Castings 

Medium 
Castings 

Soft 
Castings 

Tensile  strength  in  Ib.  per  square  inch  
Elastic  limit  in  Ib  per  square  inch 

85,000 
38,500 

70,000 
31,500 

60,000 
27,000 

Elongation  percentage  in  2  inches  
Reduction  of  area  per  cent.  .  .... 

15 

20 

18 
25 

22 
30 

WORKING  STEEL  INTO  SHAPE  119 

A  chemical  composition  which  has  given  good  results  for  locomotive 
side  frames  analyzed  as  follows: 

Carbon 0.27     per  cent 

Manganese < 0.57 

Silicon 0.26 

Phosphorus : 0.048 

Sulphur 0.033 

Test  bars  from  this  showed  a  tensile  strength  of  68,870  pounds  per 
square  inch,  an  elastic  limit  of  36,450  pounds  per  square  inch,  an  elonga- 
tion of  20%  and  alternating  vibrations  of  4707. 

VANADIUM-STEEL   CASTINGS 

Vanadium  has  given  such  good  results  in  rolled  steels  that  it  has  been 
taken  up  by  some  of  the  steel  foundries.  In  one  case  the  usual  mixture 
gave  a  steel  showing  a  tensile  strength  of  68,580  per  square  inch,  an  elastic 
limit  of  36,290  pounds,  an  elongation  of  20%,  and  resistance  to  alternating 
vibrations  of  4706.  To  the  above  mixture  was  added  0.22%  of  vanadium. 
With  this  product  added  the  following  figures  were  obtained:  tensile 
strength,  77,160  pounds  per  square  inch;  elastic  limit,  46,450  pounds  per 
square  inch;  elongation  in  2  inches  20%,  and  resistance  to  alternating 
vibrations,  14,971. 

It  is  in  resistance  to  vibrational  stresses  that  vanadium  shows  its  great 
superiority.  The  above  tests  were  made  on  an  alternating  bending 
machine  by  gripping  the  test  bar  rigidly  at  one  end  and  bending  the 
free  end  upward  and  downward  £  inch  from  its  axis.  It  gave  a  total 
length  of  stroke  of  \  inch,  and  this  at  the  rate  of  about  30  strokes  per 
minute. 

Before  adding  vanadium  in  the  furnace  it  is  necessary  to  have  the 
oxides  all  removed  from  the  metal,  as  vanadium  has  a  great  affinity  for 
oxygen.  If  any  of  the  oxides  remain  in  the  metal,  the  vanadium  will 
scavenge  them  out  and  go  off  in  the  slag;  but  as  vanadium  is  too  expensive 
to  use  as  a  scavenger,  the  oxides  should  be  removed  as  completely  as  pos- 
sible before  it  is  added  to  the  steel. 

Many  failures  in  the  use  of  vanadium  in  the  past  have  been  due  to 
this  elusiveness  or  its  affinity  for  oxygen,  as  many  thought  that  if  they 
put  the  vanadium  in  the  steel,  it  must  be  there  after  pouring.  As  a  matter 
of  fact,  it  might  have  completely  oxidized  out  of  the  metal  and  not  given 
it  any  of  the  desirable  properties  of  which  it  is  capable. 

With  the  oxides  removed  and  other  necessary  precautions  taken, 
the  vanadium  can  be  added  with  an  assurance  that  it  will  be  in  the  metal 
when  analyzed;  or  more  correctly  speaking,  that  90%  of  it  will  show  on 
analysis,  as  a  loss  of  more  than  10%  in  the  melting  is  uncalled  for. 


120  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

In  using  the  acid  open-hearth  furnace  for  melting  steel,  the  vanadium 
is  added  to  the  mixture  just  before  tapping.  The  slag  is  raked  from  the 
top  of  the  molten  metal,  the  ferro-vanadium  thrown  in  and  the  whole 
allowed  to  stand  a  few  minutes,  so  that  the  vanadium  will  thoroughly 
mix  with  the  metal. 

As  about  40%  of  the  steel  melted  for  castings  goes  back  to  the  fur- 
nace, in  the  shape  of  risers,  gates,  and  sprues,  to  be  remelted,  the  vanadium 
is  lost  in  these,  owing  to  its  oxidizing  out  during  the  melting  process. 

TITANIUM 

Owing  to  the  difficulty  of  obtaining  the  ferro-titanium,  up  to  the  pres- 
ent time,  it  has  not  been  used  to  any  extent  in  steel  castings.  Owing  to 
its  great  affinity  for  oxygen  and  nitrogen,  it  removes  these  from  the  metal. 
This  should  make  the  steel  castings  free  from  blow-holes,  and  make  a  more 
homogeneous  metal.  That  it  does  increase  the  static  and  dynamic 
strengths,  as  well  as  the  wearing  qualities  of  steel,  without  increasing  the 
hardness,  has  been  amply  proven. 

The  ferro-titanium  is  not  an  expensive  alloying  material,  and,  as  it 
is  best  to  add  it  to  the  ladle  after  tapping,  it  is  easy  to  handle  without 
greatly  increasing  the  cost  of  castings.  After  adding  the  ferro-titanium 
the  ladle  of  metal  should  be  held  about  six  minutes  before  pouring  the 
molds,  in  order  to  give  the  titanium  a  chance  to  do  its  work.  This  does 
not  chill  it,  as  might  be  supposed,  as  titanium  has  a  tendency  to  retard  the 
cooling  of  molten  steel,  and  it  will  pour  as  freely  and  smoothly  at  the  end 
of  the  six  minutes  as  a  ladle  full  of  ordinary  steel  will  directly  after  tap- 
ping. It  also  adds  some  good  properties  to  iron  castings. 

NICKEL-STEEL    CASTINGS 

Nickel  added  to  steel  in  percentages  of  from  1.50  to  3.50  combines  a 
high  tensile  strength  and  hardness,  and  a  very  high  elastic  limit,  with 
great  ductility;  therefore  it  is  being  used  for  steel  castings  with  good 
results. 

For  some  time  it  has  been  cast  in  large  castings,  such  as  rolling  mill 
gears  and  pinions,  and  it  is  now  being  cast  by  a  few  foundries  in  small 
castings  such  as  are  used  for  automobile  parts.  It  is  difficult  to  cast 
in  castings  that  have  a  thinner  section  in  any  of  their  webs,  ribs,  etc., 
than  \  of  an  inch. 

The  ductility  which  lessens  the  tendency  to  break  when  overstrained 
or  distorted,  combined  with  the  very  high  elastic  limit,  makes  it  valuable 
for  such  parts  as  crank-shafts  on  internal-combustion  engines.  These 
have  been  cast  of  nickel  steel  and  given  satisfaction  in  use,  although 


WORKING    STEEL    INTO    SHAPE  121 

forgings  are  much  better  for  this  purpose.     Front  axles,  of  I-beam  section, 
have  also  been  used  successfully  on  automobiles. 

Nickel-steel  castings  show  a  tensile  strength  of  from  78,000  to 
88,000  pounds  per  square  inch,  an  elastic  limit  of  from  50,000  to  58,000 
pounds  per  square  inch,  an  elongation  in  two  inches  of  from  25  to  30%, 
and  a  reduction  in  area  of  40  to  48%.  This  brings  the  elastic  limit  up 
nearer  to  the  tensile  strength  than  in  the  ordinary  steel  castings  as 
well  as  increasing  this  and  the  elongation  and  reduction  of  area.  This 
would  indicate  a  greater  resistance  to  shock  and  compression  and  the 
rendering  of  castings  more  ductile  and  tough  than  those  made  of  the 
ordinary  steel. 

DIRECT   STEEL   CASTINGS 

In  this  process  the  metal  is  taken  direct  from  the  furnace  to  a  heated 
mixer  where  the  proper  materials  are  added  to  make  the  required  quality 
of  steel.  The  metal  can  be  kept  liquid  as  long  as  desired  in  the 
mixer,  and  its  chemical  properties  adjusted  by  the  addition  of  different 
materials.  The  mixer  is  kept  full  by  transferring  metal  from  the  fur- 
nace. When  the  metal  is  wanted  for  casting  the  mixer  is  tapped  and  the 
metal  run  into  ladles,  from  which  it  is  poured  into  the  molds  as  in  other 
castings. 

It  produces  a  better  and  finer  grained  metal  by  the  mixer  reducing 
the  gases  which  come  in  contact  with  the  metal  in  the  cupola  or 
furnace. 

Castings  of  direct  steel  can  be  obtained  with  guaranteed  physical 
properties  as  follows:  tensile  strength,  70,000  pounds  per  square  inch; 
elastic  limit,  35,000  pounds  per  square  inch;  elongation  in  2  inches,  25%, 
and  reduction  of  area,  40%. 

These  castings  can  be  forged,  welded  and  case-hardened,  and  will 
machine  as  easily  as  machinery  steel.  They  can  also  be  bent  freely  when 
cold  before  breaking. 

MANGANESE   STEEL   CASTINGS 

Manganese  steel  with  the  manganese  ranging  from  12  to  15%,  and 
the  carbon  contents  high,  is  being  successfully  cast  and  used  for  such 
parts  as  have  to  resist  wear  from  gritty  substances  such  as  are  encoun- 
tered in  rock  crushers  or  in  machinery  used  around  concentrators. 

Manganese  steel  has  the  peculiar  properties  of  being  so  hard  that 
it  cannot  be  machined  in  combination  with  a  malleability  which  enables 
it  to  be  headed  cold  when  made  into  rivets,  and  a  toughness  which 
gives  it  remarkable  ability  to  resist  wear  and  shock  stresses  as  well 
as  cold  bending. 


122  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

When  they  leave  the  mold  manganese  steel  castings  are  about  as 
brittle  as  cast  iron,  but  by  heating  them  to  about  1850°  F.  and  quench- 
ing in  water,  they  are  given  their  properties  of  great  toughness  and  duc- 
tility. 

Owing  to  their  being  too  hard  to  machine,  all  finishing  must  be  done 
by  grinding,  but  where  it  is  desired  to  make  a  fit  by  machining,  such  as 
boring  out  a  hub,  a  piece  of  metal  that  can  be  machined  is  placed  in  the 
mold  and  the  manganese  steel  poured  around  it.  By  making  this  piece 
with  numerous  fins  the  manganese  steel  will  shrink  around  it  so  that  it 
will  be  nearly  as  firm  as  a  solid  casting. 

The  gases  generated  in  pouring  the  metal  are  so  low  that  the  molds 
can  be  rammed  very  hard  and  with  a  fine  sand.  In  this  way  surfaces 
are  obtained  that  are  nearly  as  smooth  as  finished  castings,  and  but  little 
grinding  is  required  when  a  finished  surface  is  desired. 

Its  shrinkage  is  about  double  that  of  ordinary  steel  when  cast,  and 
it  cannot  be  cast  in  any  very  intricate  shapes,  nor  can  it  be  cast  in  any 
section  which  is  thinner  than  J  of  an  inch. 

When  properly  heat-treated  manganese  steel  castings  will  show  a  ten- 
sile strength  of  140,000  pounds  per  square  inch,  an  elastic  limit  of  55,000 
pounds  per  square  inch  and  an  elongation  in  2  inches  of  45%. 

CHROME    STEEL   CASTINGS 

Where  a  great  hardness  is  desired  such  as  that  required  in  the  manu- 
facture of  projectiles,  chromium  is  added  to  steel  that  is  to  be  cast.  This 
gives  the  metal  a  mineral  hardness  that  cannot  be  obtained  with  any 
other  alloying  material,  and  also  refines  the  grain. 

The  uses  to  which  these  castings  can  be  put  is  limited,  however,  owing 
to  the  difficulty  of  machining.  The  castings  cannot  be  made  in  any 
intricate  shapes  or  thin  sections,  owing  to  the  difficulty  of  making  the 
metal  flow  easily,  but  for  such  things  as  projectiles  no  better  steel  has 
been  found  for  casting,  and  its  use  is  increasing. 

Forging 

For  those  parts  which  cannot  be  produced  from  the  rolling-mill  shapes, 
or  have  not  the  proper  strength  when  made  in  castings,  forging  is  resorted 
to  and  there  are  several  different  ways  of  turning  out  these  forgings: 
by  hand,  under  a  steam  hammer,  in  a  hydraulic  press,  or  in  a  drop-forging 
press.  The  cost  of  these  different  methods  of  production  depends  largely 
on  the  number  of  pieces  required  of  the  same  shape,  but  the  size  of  the 
piece  to  be  forged,  as  well  as  the  components  of  the  steel,  have  an  influence 
on  which  is  the  best  as  well  as  the  cheapest  method  to  use. 


WORKING    STEEL    INTO    SHAPE  123 


FORGEABILITY    OF    DIFFERENT    STEELS 

Some  of  the  special  alloy  steels  are  very  difficult  to  forge.  Chromium 
steel  is  the  most  difficult  of  all,  owing  to  its  mineral  hardness.  If  kept 
above  220°  F.,  however,  it  can  be  forged  successfully,  and  it  should  never 
be  allowed  to  fall  below  this.  Nickel  added  to  this  steel,  giving  nickel- 
chrome  steel,  makes  it  slightly  easier  to  forge,  but  even  then  the  metal 
should  be  kept  at  a  bright  yellow  color  during  the  forging  operations. 
As  steel  melts  at  2500°  F.,  this  means  that  a  forging  of  any  size  will  need 
reheating  several  times  before  it  is  completely  formed  into  shape. 
Nickel  steels  are  more  easily  forged  than  those  mentioned  above, 
but  they  must  be  handled  carefully,  owing  to  the  tendency  of  fissures 
to  appear. 

The  vanadium  steels  are  more  easily  forged  than  either  of  these,  and 
if  due  care  is  taken  to  increase  the  heat  gradually  at  first  —  that  is, 
this  steel  should  not  be  plunged  into  the  heat  all  at  once  —  no  trouble 
will  be  experienced  afterward.  Titanium  steel  is  similar  to  vanadium  as 
to  its  forgeability,  but  it  heats  up  more  slowly  and  retains  a  forging 
heat  longer.  It  also  has  less  of  the  " hot-short"  property  than  other 
steels,  and  hence  should  forge  well. 

Silicon  in  small  percentages  does  not  affect  the  forgeability  of  steel, 
but  in  large  amounts  it  gives  steel  a  fibrous  grain,  and  is  therefore  used 
principally  for  springs.  But  in  the  last  few  years  this  steel  has  been  forged 
into  gear  blanks  to  quite  an  extent.  In  this  case  the  blanks  should  be 
made  in  the  form  of  forged  rolls,  and  not  cut  from  bars,  in  order  to  avoid 
the  fibrous  structure. 

The  aluminum,  tungsten,  manganese,  and  other  alloyed  steels  are 
not  used  to  any  extent  for  forgings,  as  those  before  mentioned  show  superior 
qualities,  and  some  of  the  last  named  are  much  higher  in  price. 

Some  of  the  carbon  steels,  particularly  those  that  are  high  in  carbon, 
cannot  be  heated  to  a  temperature  over  1800°  F.,  without  burning 
the  metal,  and  when  once  burned  it  cannot  be  returned  to  its  former 
state  without  remelting.  A  vanadium-chrome  steel  will  give  as  great 
strength  as  a  nickel-chrome,  and  can  be  forged  as  easily  as  a  0.40% 
carbon  steel. 

The  higher  the  carbon  content  the  more  danger  there  is  of  burning, 
and  a  steel  with  1%  of  carbon  is  very  difficult  to  forge  at  all,  owing  to 
the  comparatively  low  temperature  to  which  it  is  possible  to  heat  it,  and 
the  comparatively  high  temperature  at  which  the  forging  operations 
must  be  finished  without  danger  of  cracking  the  piece,  owing  to  its  brittle- 
ness.  Thus  high  carbon  steel  should  not  have  the  heat  fall  much  below 
its  highest  point  of  recalescence,  which  is  above  1650°  F.,  during  any 
of  the  forging  operations.  Those  forgings  will  be  strongest  that  are 


124  COMPOSITION    AND   HEAT-TREATMENT   OF   STEEL 

finished  just  as  the  temperature  reaches  this  point.  The  smith  must 
also  regulate  the  weight  and  effect  of  the  blows  so  that  the  forging  will 
be  finished  just  as  it  reaches  this  point.  This  will  prevent  the  formation 
of  large  crystals,  give  the  piece  a  dense,  homogeneous  grain  with  the  mol- 
ecules holding  together  with  a  high  cohesive  force,  and  result  in  the 
steel  having  an  increased  strength.  Any  kind  of  steel  can  be  forged  if  the 
proper  temperature  is  maintained  while  passing  it  through  the  different 
forging  operations,  and  the  forgings  will  be  much  stronger  than  steel 
castings,  and  in  many  cases  stronger  than  rolled  steel. 

Thanks  to  the  electric  and  autogeneous  welding  process  in  combina- 
tion with  die-forging  with  either  the  drop  hammer  or  the  hydraulic  press, 
all  of  the  highest  grades  of  alloyed  steel  can  be  turned  into  forgings  suc- 
cessfully, and  their  strengths  and  elongation  retained,  but  this  is  almost 
impossible  by  the  hand  or  hammer-forging  methods,  especially  if  welds 
are  made  necessary  by  the  shape  of  the  piece.  One  of  the  alloy  steels 
that  is  being  manufactured  into  die  forgings  has  the  following  chemical 
composition:  chromium,  1.50%;  nickel,  3.50%;  carbon,  0.25%;  silicon, 
0.25%;  manganese,  0.40%;  phosphorus,  0.025%;  sulphur,  0.03%. 

In  the  annealed  state  this  shows  the  following  physical  characteris- 
tics: tensile  strength,  120,000  pounds  per  square  inch;  elastic  limit, 
105,000  pounds  per  square  inch;  elongation  in  2  inches,  20%;  reduction 
of  area,  58%. 

When  properly  heat-treated,  that  is,  quenched  in  oil  and  drawn,  these 
characteristics  became:  tensile  strength,  202,000  pounds  per  square  inch; 
elastic  limit,  180,000  pounds  per  square  inch;  elongation  in  2  inches, 
12%;  reduction  of  area,  34%. 

EFFECT  OF  TEMPERATURE  ON  THE  GRAIN 

The  high  temperatures,  of  from  2000°  to  2400°,  that  steels  are  sub- 
jected to  when  forging  would  seem  to  indicate  that  the  metal  is  weakened 
by  overheating,  but  such  is  not  the  case,  as  forgings  show  greater  strength 
than  the  same  metal  formed  into  shape  in  any  other  way,  unless  it  be 
the  rolled  steels. 

Steel,  when  heated  to  the  above  temperatures,  coarsens  in  grain  and 
the  grain  becomes  crystalline  in  nature.  This  makes  it  so  mobile  that 
it  yields  to  distortion  by  the  crystals  sliding  past  one  another,  but  as 
the  temperature  decreases  the  mobility  of  the  mass  becomes  less,  and  less 
sliding  is  possible.  If  then  forged  the  crystals  would  crush  against  each 
other;  and  when  cool  the  crystals  themselves  will  crush. 

These  coarse  crystals,  that  are  formed  by  the  high  temperatures,  are 
reduced  by  the  hammering  process  in  the  drop-harnmer  press,  or  the 
squeezing  process  in  the  hydraulic  press,  until  the  crystalline  structure 
is  broken  up  and  a  new  grain  that  is  much  finer  takes  its  place. 


WORKING  STEEL  INTO  SHAPE  125 

If  the  piece  is  not  allowed  to  cool  below  its  highest  recalescence  point 
during  the  forging,  and  the  forging  is  finished  just  as  it  reaches  that  point, 
or  a  little  above  it,  a  new  grain  structure  is  formed,  that  makes  the  metal 
more  homogeneous.  This  formation  of  grain  continues,  after  the  steel 
leaves  the  press,  until  it  has  cooled  below  its  lowest  recalescent  point,  at 
which  point  it  sets,  and  no  more  change  will  take  place  until  it  is  reheated 
to  the  recalescence  point.  These  two  points  occur  in  most  steels  at  about 
1650°  and  1400°  F.,  but  some  of  the  special  alloys  show  a  wide  variation 
from  this. 

Thus  it  will  be  seen  that  if  a  forging  is  finished  while  it  is  too  hot, 
the  grain  will  be  coarse  and  crystalline  and  the  metal  will  not  have  the 
cohesive  force  that  it  should,  and  therefore  the  piece  will  not  be  as  strong 
as  a  forging  should  be.  On  the  other  hand,  if  it  is  hammered,  or  squeezed, 
in  a  forging  press  after  it  has  become  too  cold,  the  crystals  will  be  crushed 
and  the  result  will  be  the  same,  but  if  it  is  forged  at  the  proper  heat,  the 
grain  will  be  fine,  dense,  and  homogeneous,  and  the  cohesive  force  will 
be  greater  than  was  the  case  before  it  was  forged.  This  will  naturally 
increase  the  tensile  strength  and  elastic  limit. 

Many  poor  forgings  are  turned  out  by  raising  the  temperature  of  the 
metal  too  suddenly.  Certain  molecular  changes  take  place  in  the  heating 
of  all  steels,  and  of  the  alloy  steels  in  particular,  which  are  liable  to  cause 
fissures  in  the  core  of  the  metal.  These  may  not  show  in  the  finished 
product  as  they  do  not  always  break  through  the  skin  or  outer  shell  of 
the  forging.  Thus,  by  heating  suddenly,  the  outer  shell  becomes  red 
before  the  core  has  had  an  opportunity  to  absorb  any  heat,  and  the  outer 
shell  expands,  causing  great  strains  on  the  core  of  the  piece.  In  the 
case  of  a  high  percentage  of  nickel  these  fissures  become  more  pronounced 
than  with  the  other  alloys. 

At  a  temperature  of  about  600°  F.,  or  a  bright  blue,  most  steels  lose  their 
ductility,  and  are  not  fitted  to  resist  strains  imposed  upon  them  by  the 
differential  expansion  of  an  unevenly  heated  metal.  Therefore  the  rise  in 
temperature  from  the  normal  to  600°  should  be  a  gradual  one,  but  after 
this  it  may  be  brought  up  to  the  forging  heat  as  quickly  as  is  desired. 

To  remove  the  internal  strains  caused  by  working  the  metal,  all  forg- 
ings, no  matter  how  they  are  made,  should  be  annealed  before  using,  as 
the  shocks  to  which  the  forging  may  be  submitted  will  concentrate  at 
the  point  where  these  internal  strains  are  the  strongest,  causing  it  to 
break  at  that  point.  The  case  is  very  similar  to  the  machinist  notch- 
ing a  bar  in  order  to  break  it.  The  heat  treatment  that  is  given  the  pieces 
after  they  are  forged  is  an  important  factor,  if  the  greatest  strength  and 
the  best  wearing  qualities  are  to  be  given  the  metal,  as  the  best  forgings 
can  be  ruined  by  improperly  heat-treating  them  afterward. 

Small  forgings  are  usually  tumbled,  and  large  ones  pickled  in  a  diluted 


126  COMPOSITION   AND    HEAT-TREATMENT   OF    STEEL 

solution  of  sulphuric  acid  to  remove  the  hard  outer  skin  or  scale  that 
the  finished  forgings  have.  This  is  done  so  they  can  be  machined  more 
easily,  as  this  skin  or  scale  has  a  mineral  hardness  that  will  dull  cutting 
tools  very  quickly. 

Forgings  that  are  made  with  a  knowledge  of  metals,  temperatures, 
etc.,  and  with  the  proper  skill  and  care,  are  stronger,  and  will  stand  the 
strains  and  stresses  that  are  put  upon  them  much  better  than  the  same 
steel  when  formed  into  shape  in  any  other  way,  unless  it  be  the  rolled 
stock,  which  should  be  worked  under  the  same  temperatures. 

HAND    FORGING 

When  small  pieces  and  but  few  of  a  kind  are  wanted,  hand  forging 
is  undoubtedly  the  cheapest;  but  for  large  pieces,  or  where  a  large  quan- 
tity is  wanted,  hand  forging  is  the  most  expensive  way  of  producing  them 
and  the  strength  is  not  apt  to  be  as  great  as  by  any  of  the  other  methods. 
With  a  blacksmith  shop  properly  equipped,  a  skilled  smith  can  make 
forgings  that  are  stronger  than  a  rolled  bar  from  the  same  ingot.  To 
do  this  the  piece  must  be  hammered  between  the  proper  temperatures, 
which  varies  with  the  different  grades  of  steel. 

The  steel  that  is  the  best  adapted  for  forging  under  the  hammer  has 
about  the  following  composition:  carbon,  0.15%;  silicon,  0.20%;  man- 
ganese, 0.52%;  phosphorus,  0.06%;  sulphur,  0.04%.  This  steel  in  the 
annealed  state  will  show  the  following  physical  characteristics:  tensile 
strength,  55,000  pounds  per  square  inch;  elastic  limit,  30,000  pounds  per 
square  inch;  elongation  in  8  inches,  29%;  reduction  of  area,  60%.  When 
fractured  it  will  show  a  silky  fiber. 

But  for  many  purposes  a  steel  of  much  greater  strength  than  this 
must  be  hand-forged  and  then  it  becomes  necessary  for  the  smith  to 
understand  the  nature  of  its  component  parts  so  he  can  forge  it  success- 
fully, as  many  of  the  high-grade  alloy  steels  can  be  rendered  no  better 
or  stronger  than  the  ordinary  carbon  steels  by  over  or  under  heating 
and  poor  workmanship. 

In  many  cases  welds  are  absolutely  necessary  to  produce  the  required 
shapes,  and  a  steel  of  the  following  composition  is  the  best  suitable  for 
welding:  carbon,  0.080%;  silicon,  0.035%;  manganese,  0.110%;  phos- 
phorus, 0.012%;  sulphur,  0.007%.  In  the  annealed  state  it  should  show 
the  following  physical  characteristics:  tensile  strength,  48,000  pounds 
per  square  inch;  elastic  limit,  25,000  pounds  per  square  inch;  elongation 
in  2  inches,  27%;  reduction  of  area,  69%. 

STEAM-HAMMER   FORGING 

For  pieces  of  considerable  size  and  bulk  the  steam-hammer  is  sub- 
stituted for  the  hand-forging  process.  These  hammers  vary  in  size, 


WORKING  STEEL  INTO  SHAPE  127 

from  the  small  Bradley  cushioned  hammer  that  strikes  a  blow  of  about 
500  pounds,  as  shown  in  Fig.  55,  to  those  that  strike  a  blow  of  many 
tons,  as  illustrated  by  Fig.  56,  which  is  that  of  an  8-ton  hammer,  in  use 
at  the  Bethlehem  Steel  Works.  While  this  is  not  the  largest  hammer  in 
use,  it  is  about  as  large  as  is  practical,  owing  to  the  difficulty  of  building 
a  foundation  that  will  prevent  buildings  near  it  from  being  wrecked, 
and  other  machine  foundations  ruined.  Another  style  of  steam  hammer 
is  shown  in  Fig.  57.  This,  however,  is  usually  used  for  drop  forgings. 

In  this  method  of  forging,  the  hammer  should  be  of  a  size  to  suit  the 
size  of  the  work.  The  hammer-man  must  exercise  a  good  deal  of  skill 
and  judgment  as  to  the  power  and  speed  of  the  blows  delivered  to  the 


FIG.  55.  —  Bradley  cushioned  hammer. 

piece,  as  a  too  powerful  blow  will  crush  it,  and  in  the  case  of  a  high  per- 
centage of  nickel,  fissures  and  cracks  are  liable  to  develop  which  it  will 
be  difficult  to  get  out,  and  which  may  show  in  the  finished  product. 

This  is  especially  true  if  the  piece  is  allowed  to  fall  below  the  forging 
temperature,  or  if  the  blows  are  not  distributed  evenly.  If  the  blows  are 
from  a  light  trip-hammer,  delivered  at  high  speed,  only  the  surface  of 
the  metal  will  be  bruised  and  the  core  not  affected,  thus  causing  the  core 
to  be  coarse-grained  without  the  proper  cohesion  to  insure  the  necessary 
strength. 

With  a  heavy  hammer,  descending  at  a  low  speed  on  work  that  is  held 
at  the  proper  temperature,  the  force  of  the  blow  will  penetrate  the  mass  to 
the  center  and  allow  the  particles  of  metal  to  flow  to  their  proper  position, 
insure  a  fine  grain  of  even  texture  and  be  uniform  throughout  its  entire  size. 

The  keeping  of  the  heat  to  a  good  forging  temperature  is  more  difficult 


128 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


than  in  the  hand-forgings,  owing  chiefly  to  the  difference  in  the  size  of 
the  piece  forged,  as  the  hand-forged  piece  is  usually  small  enough  for 
the  smith  to  put  in  the  fire  and  reheat  the  minute  the  temperature  falls 
below  the  best  forging  heat.  But  the  hammer-forged  piece  is  many  times 
large  enough  to  be  handled  with  a  crane,  and  is  therefore  liable  to  be  kept 
under  the  hammer  as  long  as  a  blow  will  have  any  effect  on  it. 


FIG.  56.  —  Steam  forging  hammer,  8- ton. 

This  results  in  a  very  uneven  structure,  as  when  the  metal  is  hot  the 
blows  will  penetrate  to  the  center,  and  as  it  cools  they  have  less  and  less 
penetration  until  only  the  skin  is  affected,  and  the  annealing,  which  is 
resorted  to  afterward,  cannot  bring  it  back  to  the  proper  homogeneity, 
as  some  parts  will  have  a  denser  grain  than  others,  and  therefore  be 
stronger. 


WORKING  STEEL  INTO  SHAPE 


129 


The  effect  on  the  metal  when  the  blows  are  not  powerful  enough  to 
penetrate  to  the  center,  or  the  steel  is  not  hot  enough  to  allow  them  to 
do  so,  is  shown  in  Figs.  58  and  59.  When  too  light  a  hammer  is  used, 
the  effect  shown  in  Fig.  60  is  usually  obtained.  These  same  effects  are 
often  encountered  in  drop  forgings  arid  hand  forgings,  as  well  as  in  steam- 
hamrner  forgings.  They  are  generally  overcome  by  the  use  of  a  hydraulic 


FIG.  57.  —  Erie  steam  hammer. 

forging  press,  as  with  the  press  the  metal  is  squeezed  and  consequently 
must  be  hot  enough  to  flow  into  shape,  and  this  affects  it  clear  to  the  center. 

DROP-HAMMER   FORGING 

When  enough  pieces,  of  one  shape,  are  wanted  to  warrant  making  a 
set  of  dies,  the  cheapest  and  best  way  of  producing  these  in  either  the  com- 
mon carbon  or  high-grade  alloy  steels  is  by  the  drop-forging  process.  They 
can  then  be  made  in  one  piece  without  welds,  except  in  pieces  which  are 
many  times  longer  than  a  section  through  them,  and  these  are  so  difficult 


130 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


to  keep  at  the  proper  temperature  that  they  are  usually  forged  in  two 
or  more  pieces  and  then  electrically  welded  together.     The  oxy-acetylene 


FIG.  58.  —  Effect  of  hammer  forging. 

blowpipe  has  also  been  brought  into  use  for  welds  of  this  character, 
as  well  as  for  other  forms  of  welding,  and  good  results  are  being 
obtained. 


FIG.  59.  —  Another  sample  of  hammer  forging. 

A  good  illustration  of  this  is  the  front  axle  of  an  automobile,  which 
is  usually  forged  in  I-beam  section,  4  inches  from  the  top  to  the  bottom 
of  the  I,  2J  inches  across  the  flange,  with  the  web  J  of  an  inch  thick,  and 


WORKING   STEEL  INTO  SHAPE 


131 


a  length  of  from  48  to  54  inches.  These  are  generally  forged  in  two  halves 
and  electrically  welded  in  the  center,  but  a  few  of  them  are  forged  in  one 
piece,  although  the  first  cost  of  the  dies  and  the  liability  of  their  breaking, 
owing  to  the  axle  cooling  before  the  forging  operation  is  completed,  has 
made  this  method  very  expensive. 

The  dies  that  are  necessary  for  this  kind  of  forging  are  usually  made 
of  a  60-point  carbon  steel  and  in  two  halves:  an  upper  and  a  lower  one. 
They  are  generally  parted  on  the  center  line;  but  the  shape  of  the  piece 
controls  the  location  of  the  parting  line.  The  upper  half  of  the  die  is 
fastened  to  a  ram  that  is  connected  to  the  piston  in  a  steam  cylinder, 
and  this  is  used  as  a  hammer  to  strike  the  hot  steel,  held  over  the  lower 
half  of  the  die,  a  series  of  blows.  This  forces  the  metal  to  fill  both  halves 
of  the  die,  and  thus  the  piece  is  formed  into  shape.  Dropping  the  upper 
half  die  onto  the  lower  with  a  hammer-like  blow  has  given  this  kind  of 
forging  the  name  of  drop  forgings. 


FIG.  60.  —  Piece  forged  with  relatively  light  hammer. 

The  dies  are  always  given  from  5°  to  7°  draft,  so  the  forging  will  fall 
out  easily,  and  they  are  left  open  on  the  parting  line  from  f  to  f  of  an 
inch,  according  to  the  amount  of  metal  in  the  forging.  The  amount  of 
stock  is  always  greater  than  in  the  finished  forging,  so  it  will  completely 
fill  the  die,  and  the  surplus  is  squeezed  out  at  the  opening  on  the  parting 
line.  This  fin  is  afterward  trimmed  off.  With  hard  or  brittle  steels  it 
is  best  to  make  the  dies  with  shorter  steps  between  the  different  pairs 
than  for  the  ordinary  carbon  steels. 

One  of  the  first  and  most  important  points  in  die  forging  is  the  setting 
of  the  dies,  as  the  upper  half,  which  is  fastened  to  the  ram,  and  the  lower 
half,  which  is  fastened  to  the  anvil  block,  must  come  exactly  in  line  to 
produce  a  perfect  forging. 

The  lower  half  of  the  die  should  have  a  current  of  air  blowing  in  it 
that  is  strong  enough  to  remove  all  of  the  scale  that  works  off  from  the 


132 


COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 


piece  being  forged.  The  air  blast  should  be  directed  so  it  will  not  cool 
the  hot  metal  while  being  forged.  Steel-wire  brushes  can  be  used  for 
this  purpose,  but  the  air  is  quicker,  and  if  well  adjusted  is  more  positive. 
The  upper  half  of  the  die  should  be  kept  well  oiled  so  the  scale  will  not 
stick  to  that.  This  can  be  done  by  rubbing  a  swab,  well  soaked  in  oil, 
through  the  die  every  time  it  is  raised  off  the  work. 

With  the  dies  properly  set  and  the  press  adjusted  so  the  two  dies  will 
come  together  on  the  parting  line,  the  work  can  be  turned  out  to  one 
thirty-second  of  an  inch  of  the  finished  size,  thus  making  much  less  machine 


FIG.  61.  —  Different  operations  on  forging  a  crank-shaft. 

work  than  by  the  hand  or  steam-hammer  forging  processes,  and  when 
grinding  is  to  be  used  in  finishing,  the  work  can  be  brought  to  within  one 
one-hundredth  of  an  inch. 

The  cost  of  drop  forgings  depends  on  the  number  needed,  and  the  num- 
ber that  can  be  turned  out  at  one  setting  of  the  dies,  as  well  as  on  the 
quality  of  the  steel  used. 

Some  of  the  largest  pieces  that  are  being  made  by  drop  forging  are 
the  crank-shafts  for  internal  combustion  engines,  and  the  different  opera- 
tions in  forging  these  are  shown  in  Fig.  61.  At  A  is  shown  the  straight 
bar,  cut  to  the  proper  length.  This  is  first  bent  to  the  shape  shown  at 
B  in  the  bending  press.  It  is  then  drop-forged,  and  when  it  leaves  the 
dies,  it  is  similar  to  the  piece  shown  at  C.  The  dies  are  usually  left  J 


WORKING  STEEL  INTO  SHAPE 


133 


inch  apart  on  the  parting  line  for  this  size  of  forging,  to  allow  the  excess 
metal  to  squeeze  out  between  them,  which  forms  into  the  fin  that  is  shown 
at  C.  This  necessitates  the  making  of  an  extra  pair  of  dies  for  shearing 
off  the  fins.  After  this  is  done  the  crank  has  the  appearance  of  that 
shown  at  D.  On  this  particular  shaft  there  was  a  comparatively  large 
flange  on  one  end,  as  shown  in  E.  This  would  be  difficult  to  form  in 
the  dies  when  forging  the  rest  of  the  shaft,  and  for  this  reason  an  extra 
amount  of  metal  is  left  on  the  shaft  at  this  point  and  the  flange  is  formed 


FIG.  62.  —  Taking  crank-shaft  from  furnace  to  hammer  for  first  operation. 

in  another  set  of  dies  after  the  rest  of  it  has  been  forged.  This  com- 
pletes the  forging  operations  and  the  shaft  is  ready  to  be  machined;  the 
machined  crank-shaft  being  shown  at  F. 

One  of  the  largest  drop  forgings  that  has  so  far  been  made  (June,  1910) 
is  a  two-throw  crank-shaft,  made  by  the  Bethlehem  Steel  Company,  that 
when  finished  weighs  400  pounds.  The  operations  are  similar  to  those 
shown  in  Fig.  61.  Fig.  62  shows  the  piece,  after  it  has  been  bent  and 
heated,  as  it  is  being  taken  from  the  furnace  to  the  5000-pound  drop- 
hammer  for  the  first  operation.  Back  of  the  furnace  can  be  seen  the  top 
of  the  bending  press,  which  bends  the  straight  bar  to  the  shape  shown  by 


134 


COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 


the  partially  forged  crank  in  Fig.  64.  Fig.  63  shows  the  piece  being  held 
under  the  hammer  ready  to  drop  the  die  on  it.  Fig.  64  shows  the  crank- 
shaft after  it  has  been  partly  formed  and  as  it  is  being  taken  back  to  the 
furnace  to  be  reheated  for  the  final  forging  operation  under  the  hammer. 
Fig.  65  shows  the  crank-shaft  as  it  was  being  taken  out  of  the  dies  after 


FIG.  63. — 400-pound  crank-shaft  under  hammer  ready  to  drop  the  die. 

the  final  forming  operation.     In  front  of  the  hammer  is  shown  a  finished 
crank-shaft  with  a  5-foot  rule  standing  beside  it  to  show  its  length. 

An  idea  of  the  variet}^  of  shapes,  sizes,  and  styles  of  machine  parts 
that  can  be  economically  made  by  the  drop-forging  process  can  be  obtained 
from  Fig.  66.  At  the  lower  edge  of  the  half-tone  is  laid  a  5-foot  folding 
rule,  and  just  above  it  is  the  400-pound  crank-shaft  that  has  just  been 


WORKING  STEEL  INTO  SHAPE 


135 


described  in  its  forging  operations;  while  at  the  top  of  the  picture  are 
forgings  that  will  require  about  twenty  to  weigh  one  pound. 


PRESSED    FORGINGS 


The  inferior  quality  of  many  die  forgings  is  undoubtedly  due  to  the 
drop-hammer  process,  as  this  has  a  tendency  to  produce  only  a  bruising 


FIG.  64.  —  Removing  partially  forged  400-pound  crank-shaft. 

effect,  owing  to  the  top  die  descending  at  a  high  speed  and  deliver- 
ing a  light  blow  which  has  no  penetration.  The  hydraulic,  pneumatic 
or  steam  press,  on  the  other  hand,  produces  forgings  of  a  far  superior 
quality  because  it  slowly  squeezes  the  metal  into  the  shape  of  the  die, 
thus  allowing  it  more  time  to  flow  into  place  and  assume  its  new  shape, 


136 


COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 


and  therefore  making  it  more  uniform  in  quality  and  with  less  internal 
strains. 

With  the  hammer  blow  in  forging  a  wavy  grain  is  obtained,  as  shown 
in  Figs.  58  and  59,  i.e.,  directly  under  each  blow  of  the  hammer  a  dense 
grain  is  produced,  while  around  the  edge  of  the  blow  it  is  less  dense.  This 
causes  the  ridges  shown  in  the  fracture  of  the  fine-grained  metal  around 
the  outside  of  the  bar.  In  conjunction  with  this  is  the  inability  of  the 
blow  to  penetrate  to  the  center.  In  one  or  two  places,  where  one  blow 
did  not  overlap  another,  the  shape  of  the  metal  affected  by  the  blow  can  be 
plainly  traced.  Where  the  steel  is  pressed  or  squeezed  into  shape  this 


FIG.  65.  —  Final  forging  operation. 

variation  in  the  density  of  the  grain  of  the  piece  would  not  show,  and  it 
would  be  condensed  clear  to  the  center,  as  the  steel  being  operated  on  would 
have  to  be  hot  enough  to  flow  into  the  shape  desired  under  the  high  pres- 
sure used,  or  it  could  not  be  worked. 

That  the  press  makes  a  more  homogeneous  metal  than  the  hammer, 
or  even  the  rolls,  and  hence  a  stronger  and  tougher  one,  is  well  illustrated 
by  the  German  government  specifications  for  steel  forgings  worked  by 
rolls,  hammer,  or  press  which  says:  " Forgings  made  from  rolled  or 
hammered  steel  must  have  the  initial  section  at  least  eight  times  that  of 
the  finished  section;  while  those  made  from  pressed  steel  need  have  an 
initial  section  only  four  times  the  finished  section." 


WORKING   STEEL   INTO   SHAPE 


137 


138 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


With  the  press,  rounds,  flats,  squares,  and  irregular  shapes  can  be 
forged  without  dies,  as  with  the  steam  hammer,  or  two  halves  of  a  die 
can  be  pressed  together  to  make  die  forgings,  the  same  as  with  the  drop 
hammer.  When  forging  metal  into  shape,  a  much  greater  force  can  be 
brought  against  it,  with  the  press,  than  with  the  hammer,  owing  to  the 


FIG.  67.  —  A  1400-ton  forging  press. 

absence  of  any  jarring.  As  a  consequence  of  this  the  steel  works  are  all 
adopting  presses  for  their  heavier  work.  Some  of  these  operate  at  a  very 
high  speed,  when  compared  with  the  hydraulic  presses  of  a  few  years 
back. 

The  power  behind  the  press  is  obtained  by  the  use  of  either  water, 
air,  or  steam,  but  the  hydraulic  press  is  the  one  that  has  been  almost 
universally  adopted.  A  large-sized  press  of  this  kind  is  shown  in  Fig.  67. 


WORKING  STEEL  INTO   SHAPE 


139 


This  is  a  14,000-ton  press  at  work  on  a  forging,  but  it  is  typical  of  the 
style  of  hydraulic  presses,  and  they  can  be  obtained  in  much  smaller  sizes. 


FIG.  68.  —  Small  high-speed  steam-hydraulic  forging  press. 

In  place  of  the  upper  and  lower  press  blocks  used,  others  can  be  inserted 
that  will  form  rounds,  octagons,  etc.,  or  the  two  halves  of  a  die  can  be 
put  in  their  place  to  form  irregular  shaped  pieces. 


140 


COMPOSITION  AND   HEAT-TREATMENT   OF  STEEL 


A  combination  of  the  steam-hammer  and  hydraulic  press  has  recently 
been  placed  on  the  market,  and  this  promises  to  have  a  very  useful  field. 


FIG.  69.  —  Large  high-speed  steam  hydraulic  forging  press. 

One  of  the  smaller  sizes,  with  a  single  frame,  that  is  built  in  sizes  from 
150  to  400  tons,  is  shown  in  Fig.  68,  and  a  large  size  with  four  columns,  in 
sizes  from  300  to  12,000  tons,  is  shown  in  Fig.  69.  These  machines  raise  the 


WORKING  STEEL  INTO  SHAPE 


141 


ram  and  lower  it  onto  the  work,  which  can  be  done  with  a  blow  if  desired, 
and  then  the  water  pressure  is  turned  on  to  squeeze  the  piece  into  shape. 
It  also  can  be  used  with  or  without  finished  dies  in  the  making  of  forgings. 

With  the  hydraulic  press  it  is  possible  to  make  simple,  inexpensive 
dies  that  will  forge  quite  complicated  pieces.  Pieces  that  are  impossible 
to  make  in  the  drop-hammer  and  are  very  expensive  to  make  by  hand- 
forging  can  be  made  remarkably  cheaply  and  accurately.  As  an  example 
of  this,  the  piece  shown  in  Fig.  70,  after  the  machine  work  was  done,  was 
forged  in  a  hydraulic  press  with  the  apparatus  described  below. 


FIG.  70.  —  Wheel  hub  to  be  forged  in  hy- 
draulic press. 

A  piece  of  3£-inch  round  stock  was  cut  the  required  length  and  put 
in  the  die,  as  shown  at  G  in  Fig.  71.  Here,  A  is  the  die-holder;  C  the  die 
block,  which  is  put  in  loose,  and  E  the  flanging  punch.  A  loose  block 
is  put  under  the  piece  G  and  when  it  leaves  the  press  it  is  the  shape 
shown  in  Fig.  72.  The  next  operation  is  to  punch  out  the  center  and 
spread  out  the  top  to  form  the  shoulder,  and  this  is  shown  in  Fig.  73. 
Here  the  die  in  Fig.  71  has  had  the  loose  block  in  the  bottom  taken  out, 
and  the  two  halves  of  the  die  block,  D,  B  (Fig.  73),  placed  on  top  of  the 
forging.  When  the  punch  is  pressed  down  it  forms  the  piece  into  the 
shape  shown  in  Fig.  74,  and  when  the  bottom  of  this  is  trimmed  off  it 
leaves  |  of  an  inch  finish  all  over. 


142 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


Thus,  while  the  press  makes  f orgings  with  much  better  metal  than  those 
turned  out  with  any  kind  of  a  hammer,  it  also  presents  greater  possibili- 


Top  Platen  of  Press 


Punch  Holder 


Flanging  Punch 


Die  Holder 


Bottom  Platen  of  Press 

FIG.  71.  —  Stock  in  die  ready  for  first 
operation. 

ties  to  the  maker  and  user  of  forgings  in  the  way  of  difficult  shapes  that 
can  be  economically  made.  The  example  given  is  merely  one  of  a  large 
variety  of  shapes  that  can  be  made  in  a  similar  way  with  the  use  of  loose 


FIG.   72.  —  Cross-section   of  forging  after 
first  operation. 

dies.  Fig.  75  shows  a  few  more  shapes  that  have  been  made  in  the 
hydraulic  press;  some  of  which  were  made  with  loose  die  blocks,  and  these 
will  doubtless  suggest  to  the  student  many  more  that  can  be  made. 


WORKING  STEEL  INTO  SHAPE 


143 


Top  Platen  of  Press 

w///////////////^^^^ 


v////////////////////////////////////^ 

Bottom  Platen  of  Press 

FIG.  73.  —  Forging  in  die  ready  for  second 
operation. 


Recess  la  formed  by 
large  Shoulder  on  Puncb  F 


W/////////////////A 


The  Part  below  Line  la 
Cut  off  leaving  a  Forging 
with  a  Hole  directly 
through  it. 


FIG.  74.  —  Forging  after  second  operation, 
ready  for  machine  shop. 


144 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


Welding 

In  many  of  the  more  intricate  shapes  that  are  hand-forged,  resource 
is  had  to  welding,  and  if  the  average  smith  were  told  that  he  could  not 
make  a  perfect  weld  he  would  feel  greatly  insulted.  But  from  a  large 
number  of  so-called  perfect  welds  that  were  examined  very  few  showed 
a  strength  equal  to  50%  of  the  unwelded  section.  With  the  alloy  steels 
it  is  difficult  to  get  a  weld  that  will  even  show  that  percentage,  as  nickel, 
chromium,  vanadium,  tungsten,  aluminum,  and  some  other  alloys  do 
not  lend  themselves  to  the  welding  process.  It  is  difficult  to  make 
welds  at,  all  by  the  hand  methods  in  a  blacksmith's  forge,  when  these 


FIG.  75.  —  More  shapes  made  in  hydraulic  press  with  loose  die  blocks. 

elements  are  ingredients  of  the  steel  to  be  welded.  Some  of  these  steels 
have  been  welded,  but  an  efficiency  of  over  25%  is  seldom  obtained. 

Carbon,  however,  is  the  principal  enemy  of  welds,  and  with  this  as 
low  as  0.15%  it  must  be  handled  with  great  care  at  the  welding  heat, 
while  with  0.20%  of  carbon  the  steel  is  very  unreliable,  and  with  0.50% 
of  carbon  the  steel  is  liable  to  be  burnt  at  a  temperature  well  below  the 
welding  heat. 

Thus  to  make  hand-forgings  where  welds  are  necessary,  the  pieces 
must  be  from  two  to  three  times  the  size  of  that  necessary  for  the  required 
strength,  and  with  some  of  the  alloyed  steels  even  this  will  not  suffice. 


PRINCIPLES    INVOLVED 


Welding  consists  of  heating  two  pieces  to  a  high  temperature,  then 
dissolving  off  the  iron  oxide,  which  has  formed  on  the  surface,  by  the  use 


WORKING  STEEL  INTO  SHAPE  145 

of  some  flux,  such  as  borax,  and  then  firmly  pressing  the  pieces  together. 
Welding  plates  are  sometimes  put  between  the  pieces  to  be  welded  in 
place  of  the  borax.  These  are  special  preparations  which  are  made  for 
this  purpose,  and  are  covered  by  patents. 

The  exact  temperature  at  which  to  heat  pieces  for  welding  is  not  known, 
but  it  is  near  the  melting  point,  as  the  steel  must  be  in  a  soft,  almost 
pasty,  condition.  The  pieces  are  usually  upset  or  enlarged  at  the  ends, 
so  that  the  section  at  the  weld  will  be  larger  than  the  rest  of  the  piece. 
In  the  ordinary  weld  they  are  hammered  continuously  until  the  metal  has 
cooled  to  a  dull  red.  This  breaks  up  the  coarse  crystals  which  have  been 
produced  by  the  high  temperature,  and  by  finishing  at  a  low  temperature 
a  small  grain  is  secured. 

This  small  grain  is  obtained,  in  the  metal  close  to  the  weld,  by  proper 
welding,  but  there  is  always  a  place  within  a  short  distance  of  the  weld 
that  must  have  been  heated  to  a  high  temperature,  which  means  over- 
heated, and  has  not  received  the  mechanical  treatment  given  at  the  weld 
by  hammering  it  down  to  the  proper  finishing  temperature.  This  will 
cause  the  metal  to  have  a  coarse  grain  at  this  point,  which  is  usually  from 
4  to  8  inches  from  the  weld,  and  the  steel  to  break  when  submitted  to 
strain. much  less  than  the  original  strength  of  the  metal  welded.  Thus, 
while  the  average  welder  may  say  that  if  no  break  occurs  at  the  weld 
it  is  as  strong  as  the  original  piece,  this  is  not  true  and  welds  are  seldom 
made  by  hand  methods  that  have  more  than  60%  of  the  efficiency  of 
the  original  piece.  In  a  large  number  of  tests  which  were  made  it  was 
found  that  the  chief  cause  of  damage  was  the  bad  crystallization  adjacent 
to  the  weld. 

All  steels  that  have  been  welded  would  give  better  results  if  they  were 
reheated  to  a  little  above  1650°  F.,  as  this  heating  would  restore  to  a  large 
extent  the  grain  size  of  all  parts. 

Steel  is  burned  when  the  first  drops  of  melted  metal  begin  to  form 
in  the  interior  of  the  mass.  These  segregate  to  the  joints  between  the 
crystals  and  cause  weakness.  The  second  stage  of  this  is  when  the  molten 
drops  segregate  as  far  as  the  exterior  and  leave  behind  a  cavity  filled 
with  gas.  The  third  and  last  stage  is  reached  when  gas  collects  in  the 
interior  under  sufficient  pressure  to  form  miniature  volcanoes  and  break 
through  the  skin.  This  projects  liquid  steel  and  produces  the  well-known 
scintillating  effect  of  this  temperature.  Into  the  openings  formed  by 
these  miniature  explosions  air  enters  and  oxidizes  the  interior.  Steel  that 
has  been  overheated  to  this  extent  cannot  be  fully  restored  by  either 
mechanical  working  or  heat  refining. 


146  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


ELECTRIC   WELDING 

The  hand  method  of  welding  being  a  slow,  laborious  process  when 
large  pieces  were  to  be  welded,  and  the  efficiency  of  the  welds  being  low, 
it  became  necessary  to  abandon  welding,  in  many  cases,  as  a  commercial 
possibility,  or  to  invent  some  other  means  of  performing  the  welding 
operation.  This  necessity  brought  into  use  two  electrical  welding  processes 
and  several  gas  processes. 

In  the  electrical  resistance  process  the  pieces  to  be  welded  are  usually 
butted  together  and  clamped  so  there  will  be  a  pressure  against  each  other. 
Two  electrodes  are  then  placed  on  each  side  of  the  joint  to  be  welded,  and 
the  current  of  electricity  passing  through  these  also  passes  through  the 
steel  at  the  joint.  This  softens  the  metal  by  heating  it  nearly  to  the 
melting  point,  and  the  pressure  of  one  piece  against  the  other  squeezes 
them  together  until  they  are  welded. 

This  process  has  many  advantages  over  the  hand  method.  The 
heating  can  be  localized  and  held  in  the  immediate  vicinity  of  the  weld, 
and  the  hand  can  be  held  on  the  metal  but  a  very  few  inches  back  from 
the  weld.  This  prevents  the  metal  from  crystallizing  6  or  8  inches  back 
as  in  the  forge-heated  piece;  the  temperature  of  the  surfaces  to  be  welded 
is  always  under  control,  which  reduces  the  danger  of  overheating  the 
steel  to  a  minimum.  The  pressure  between  the  abutted  pieces  may 
be  regulated  to  any  pressure  desired  and  very  irregular  shapes  may  be 
butted  together  and  welded  in  a  very  accurate  manner.  The  efficiency 
of  the  weld  has  been  increased  50%,  and  in  some  cases  100%  over  that 
of  hand  welding. 

The  other  electric  welding  process  is  called  arc  welding.  In  this  a 
carbon  electrode  is  placed  in  a  holder  so  it  can  be  held  in  the  hand  close 
to  the  work,  which  is  placed  on  an  iron  or  steel-topped  table.  This  table 
is  connected  to  a  rheostat,  and  that  to  the  power  supply,  as  is  also  the 
carbon  electrode.  A  water  rheostat  is  usually  used.  With  the  proper 
connections  made,  the  electric  current  flows  through  the  rheostat  and  the 
carbon  electrode  and  strikes  an  electric  arc,  the  same  as  do  the  arc  lamps 
seen  in  the  street.  This  creates  an  intense  heat  that  melts  the  metal 
on  each  side  of  the  joint,  and  by  holding  a  rod  in  the  other  hand,  new 
metal  can  be  fused  with  the  old  metal  in  the  joint,  and  the  two  pieces 
stuck  together. 

This  is  a  process  of  casting  steel  into  the  joint,  and  hence  rolled  or 
forged  metal  cannot  be  made  as  strong  as  the  original  stock  except  by 
leaving  a  ridge  at  the  weld,  so  the  metal  will  be  thicker.  Even  this, 
however,  will  make  a  stronger  weld  than  can  be  made  by  the  blacksmith 
with  a  hammer,  anvil,  and  forge  fire.  If  the  arc  electric  welds  were  ham- 
mered after  welding,  while  the  metal  was  still  hot,  and  before  it  had  cooled 


WORKING  STEEL  INTO  SHAPE  147 

to  a  dull  red,  the  weld  could  be  made  much  stronger,  as  this  would  change 
the  grain  from  the  coarse  crystalline  one  of  a  casting  to  the  more  dense 
grain  that  approaches  that  of  a  forging. 

Alloyed  steels  that  do  not  lend  themselves  readily  to  welding  by  hand 
can  be  successfully  welded  by  the  electrical  process.  The  density  of  the 
metal  is  much  more  uniform  when  welded  by  electricity  than  by  the  hand 
method,  and  the  weld  is  made  in  a  fraction  of  the  time.  The  amount 
of  work  required  in  finishing  after  electric  welds  is  very  small,  as  it  leaves 
it  comparatively  smooth;  a  slight  ridge  right  at  the  weld  being  practically 
all  the  deformation  there  is  in  the  metal. 

This  has  aided  greatly  in  the  production  of  forgings,  as  they  can  be 
made  in  two,  three,  or  more  pieces  and  afterward  welded  together.  It 
has  also  been  found  in  many  cases  to  be  a  better  method  than  brazing,  and 
is  sometimes  substituted  for  this. 

WELDING   WITH   GASES 

Several  different  processes  of  welding  with  gases  and  a  blowpipe 
or  torch  have  recently  been  developed,  and  these  have  become  quite  a 
factor  in  the  manufacture  and  repair  of  metal  parts  of  all  kinds.  The 
gases  used  for  these  various  processes  are  acetylene,  hydrogen,  liquid 
gas,  city  gas,  and  natural  gas,  which  are  burned  either  with  oxygen 
or  with  air.  All  of  these  processes  operate  in  the  same  way  as  the 
arc  electric;  i.e.,  they  melt  new  metal  into  the  joint  and  fuse  it  with 
the  old. 

Of  the  several  gas  processes  the  oxyacetylene  has  taken  the  lead, 
and  this  consists  of  heating  the  metal  with  a  torch,  using  oxygen  and 
acetylene  gas.  With  this  the  metal  is  heated  to  the  melting  point,  and 
a  steel  rod  is  passed  along  with  the  flame,  when  steel  is  being  welded, 
and  the  metal  melts  off  from  the  rod  and  flows  into  the  joint  until  it  has 
been  filled. 

The  flame  is  largely  carbon  monoxide,  but  at  the  tip  where  the  heating 
takes  place  it  is  converted  into  carbon  dioxide.  This  gives  a  flame  that 
will  neither  carbonize  or  oxidize  the  metal.  In  lighting  the  blowpipe 
or  torch  the  acetylene  is  first  turned  on  full,  then  the  oxygen  is  added 
until  the  flame  has  only  a  single  cone  whose  apex  has  a  temperature  of 
about  6300°  F.  Too  much  acetylene  produces  two  cones  and  a  white 
color,  while  an  excess  of  oxygen  is  shown  by  the  flame  assuming  a  violet 
tint  and  a  ragged  end.  The  best  welding  results  are  obtainable  with 
1.7  volumes  of  oxygen  to  one  of  acetylene. 

The  oxygen  for  the  process  is  obtained  by  either  using  a  special  gen- 
erator that  generates  oxygen  from  chemicals,  or  by  buying  the  oxygen 
that  is  stored  in  steel  bottles  and  sold  in  the  open  market.  It  is  used 
at  a  pressure  of  about  15  pounds  per  square  inch.  The  acetylene  gas 


148  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

is  manufactured  in  the  ordinary  way  from  calcium  carbide,  and  used  at 
a  pressure  of  2  or  3  pounds. 

Through  a  system  of  piping,  the  flame  is  easily  carried  to  the  work, 
which  saves  the  labor  of  moving  large  pieces  of  work  to  a  forge  or  hammer 
for  welding.  Pieces  one  inch  thick  have  been  successfully  welded  with 
this  process,  but  its  best  application  is  in  welding  thinner  sheet  metal, 
as  joints  of  great  length  can  be  easily  welded.  In  fact,  its  only  limit  is 
the  length  of  the  joint  and  the  time  needed,  and  this  latter  can  be  carried 
out  indefinitely. 

Oxy acetylene  welding  gives  its  best  results  in  the  welding  of  steel, 
but  cast  iron  is  being  welded  successfully  as  well  as  copper,  brass,  and 
bronze. 

The  different  metals  can  also  be  welded  together  as  is  shown  in  Fig. 


FIG.  76.  —  Steel,  copper,  brass,  and  bronze  welded  together. 

76,  in  which  four  plates  were  butted  together  and  welded.  One  plate 
was  steel,  as  shown  by  the  white  square;  another  brass,  as  shown 
by  the  darker  square  in  the  diagonally  opposite  corner;  and  the  two 
very  dark  squares  were  copper  and  bronze  respectively.  After  welding 
these  they  were  bent  and  broken  at  the  joints  to  see  if  they  were 
thoroughly  welded,  and  from  the  appearance  of  the  fractures  they  would 
indicate  a  perfect  weld.  The  steel  welded  to  the  copper  and  bronze  as 
well  as  the  brass  did.  Owing  to  the  high  heat  of  the  flame,  however, 
some  of  the  lead  and  zinc  in  the  brass  and  bronze  melted  out,  leaving 
holes  in  the  metal. 

This  welding  process,  as  well  as  all  the  other  gas  processes,  makes  the 
weld  by  casting  metal  into  the  joint  in  the  same  way  as  does  the  arc  elec- 
tric welding  process.  Therefore,  on  rolled  or  forged  metal  the  joint  is 
not  as  strong  as  the  original  metal,  but  it  is  stronger  than  a  weld  made 


WORKING  STEEL  INTO  SHAPE  149 

with  a  forge  fire,  hammer  and  anvil,  and  metals  can  be  welded  that 
it  is  impossible  to  weld  in  the  latter  way.  In  some  cases  an  efficiency 
of  90%  has  been  claimed,  but  if  the  work  is  properly  done  an  efficiency  of 
at  least  80%  can  be  obtained  with  any  metal. 

The  oxyhydrogen  process  only  differs  from  the  oxyacetylene  in  that 
hydrogen  gas  replaces  the  acetylene  gas.  The  oxygen  and  hydrogen  are 
used  in  the  proportion  of  from  2  to  4  parts  hydrogen  to  1  of  oxygen,  and 
the  hottest  part  of  this  flame  is  about  f  of  an  inch  from  the  point  of  the 
burner. 

Two  parts  hydrogen  to  one  of  oxygen  will  give  a  flame  with  a  temper- 
ature of  about  4350°  F.,  but  if  a  flame  is  desired  with  a  reducing  action 
it  is  necessary  to  use  4  parts  of  hydrogen  to  1  of  oxygen,  and  this  will 
have  a  temperature  of  about  3450°  F.  This  flame  will  melt  iron  or  steel, 
and  cause  it  to  weld  even  if  the  surfaces  are  not  clean,  as  any  rust  present 
will  be  reduced.  It  is  also  a  very  good  flame  to  use  for  the  cutting  up 
of  metals.  This  lower  temperature  of  the  flame  is  really  better  for 
sheets  up  to  f  of  an  inch  thick,  as  the  melting  of  the  metal  is  less  rapid 
and  less  explosive,  giving  a  welded  joint  that  is  cleaner  and  with  fewer 
scars  and  blisters. 

The  oxyliquid  gas  welding  process  consists  of  replacing  the  acetylene 
or  hydrogen  with  liquid  gas,  and  as  this  combination  generates  a  heat 
of  about  4000°  F.,  it  will  make  welds  that  are  equal  to  either  of  the 
above  processes,  and  for  all  practical  purposes  it  is  as  good.  The 
liquid  gas  is  a  product  that  is  made  from  crude  oil  and  stored  in  steel 
bottles,  similar  to  oxygen,  at  a  high  pressure.  At  this  pressure  it  is  a 
liquid,  but  when  allowed  to  expand  to  the  15  pounds  pressure  required 
for  welding,  it  becomes  a  gas,  and  is  mixed  with  the  oxygen  in  a  torch, 
the  same  as  the  other  processes. 

Another  process  uses  city  or  natural  gas  and  oxygen.  These  are 
combined  in  a  torch,  to  get  the  proper  mixture  and  generate  the  neces- 
sary heat  for  welding.  For  many  purposes  this  is  very  useful,  but  the 
flame  does  not  have  as  high  a  temperature  as  the  others. 

Still  another  process  consists  of  combining  city  or  natural  gas  with 
two  blasts  of  air;  one  of  which  has  a  high  pressure  and  the  other  a  low 
pressure.  These  are  sent  through  a  special  torch  and  have  been  used  to 
successfully  weld  cast  iron  and  the  non-ferrous  metals.  It  does  not 
seem  to  develop  enough  heat  to  weld  steel,  and  therefore  its  field  seems 
to  be  limited  to  metals  of  a  lower  fusing  temperature  than  steel.  Acety- 
lene has  also  been  used  in  addition  to  the  above  gas  and  air  with  good 
results. 

THERMIT   WELDING 

The  thermit  process  of  welding  is  radically  different  from  all  the  other 
processes,  and  is  useful  for  an  entirely  different  class  of  work. 


150  COMPOSITION    AND    HEAT-TREATMENT   OF   STEEL 

In  this  process,  a  sand  mold  is  built  around  the  pieces  to  be  welded 
and  the  metal  poured  in  this.  The  mold  is  made  of  sand  and  clay,  which 
should  be  mixed  thoroughly  stiff  and  as  dry  as  possible,  as  the  less  mois- 
ture there  is  in  the  mold  the  better  will  be  the  results  obtained.  For 
this  reason  the  mold  should  be  dried  in  a  furnace  or  oven  at  a  low  tem- 
perature for  from  six  to  eight  hours.  To  test  the  dryness  of  the  mold, 
two  or  three  wires  can  be  rammed  up  in  the  thickest  section  of  it  and  these 
pulled  out  after  drying  to  see  if  any  moisture  remains. 

With  the  mold  completed  the  thermit  is  placed  in  a  special  receptacle 
which  is  located  over  the  mold.  The  thermit  consists  of  aluminum  and 
oxide  of  iron.  A  little  ignition  powder  is  placed  in  this  and  lighted  with  a 
match.  Immediately  there  sets  up  a  tremendous  chemical  action,  which 
produces  a  superheated  liquid  steel  and  superheated  liquid  slag  consisting 
of  aluminum  oxide.  When  the  mass  is  entirely  molten  it  attains  a  tem- 
perature of  5400°  F.  The  bottom  of  the  receptacle  is  then  tapped  and 
the  liquid  inetal  runs  into  the  mold  and  into  and  around  the  joint  to 
be  welded.  The  high  temperature  of  the  liquid  mass  causes  the  ends 
of  the  pieces  to  be  welded,  to  become  molten  and  pasty,  and  fuse  with 
the  thermit. 

Welds  were  made  with  this  process  on  a  bar  of  rolled  steel,  2  by  4£ 
inches,  which  was  broken,  then  welded,  and  afterwards  tested.  The  tests 
showed  an  efficiency  of  97%  in  tensile  strength  and  88%  in  elastic  limit. 

The  greatest  usefulness  of  this  method  of  welding  is  for  the  stern  frames 
of  steamships  which  have  broken,  locomotive  side  frames,  driving  wheels, 
connecting  rods,  and  other  things  of  a  similar  nature,  but  the  building 
of  the  mold  makes  it  commercially  prohibitive  where  autogeneous  or 
electric  welding  can  be  used  economically. 


CHAPTER  VIII 
FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 

IN  working  steels  it  is  very  important  that  they  be  properly  heat- 
treated,  as  poor  workmanship  in  this  regard  will  produce  working  parts 
that  are  not  good  even  though  the  stock  used  be  the  highest  grade  of 
steel  that  is  procurable.  And  by  improperly  heat-treating  them  it  is 
possible  to  make  high-grade  steels  more  brittle  and  less  able  to  support 
a  load  or  withstand  stresses  than  ordinary  carbon  steels.  All  steels  are 
improved  in  tensile  strength,  elastic  limit,  elongation,  or  reduction  of 
area  by  annealing,  hardening,  or  tempering  them.  The  different  treat- 
ments are  divided  into  three  distinct  classes,  the  first  of  which  is  harden- 
ing, the  second  annealing  and  reheating,  and  the  third  case-hardening, 
carbonizing,  or  cementing. 

The  theory  of  heat-treatment  rests  upon  the  influence  of  the  rate  of 
cooling  on  certain  molecular  changes  in  structure  occurring  at  different 
temperatures  in  the  solid  state.  These  changes  are  of  two  classes,  critical 
and  progressive;  the  former  occur  periodically  between  certain  narrow 
temperature  limits,  while  the  latter  proceed  gradually  with  the  rise  in 
temperature,  each  change  producing  alterations  in  the  physical  charac- 
teristics. By  controlling  the  rate  of  cooling,  these  changes  can  be  given 
a  permanent  set,  and  the  physical  characteristics  can  thus  be  made  differ- 
ent from  those  in  the  metal  in  its  normal  state. 

The  results  obtained  are  influenced  by  certain  factors  as  follows: 
First,  the  original  chemical  and  physical  properties  of  the  metal.  Second, 
the  composition  of  the  gases  and  other  substances  which  come  in  con- 
tact with  the  metal  in  heating  and  cooling.  Third,  the  time  in  which  the 
temperature  is  raised  between  certain  degrees,  or  the  temperature-rise 
curve.  Fourth,  the  highest  temperature  attained.  Fifth,  the  length 
of  time  the  metal  is  maintained  at  the  highest  temperature.  Sixth,  the 
time  consumed  in  allowing  the  temperature  to  fall  to  atmospheric  or 
the  temperature-drop  curve. 

The  third  and  sixth  are  influenced  by  the  size  and  shape  of  the  piece; 
by  the  difference  in  temperature  between  it  and  the  heating  and  cooling 
mediums,  and  by  the  thermal  capacity  and  conductivity  of  the  latter. 
Each  of  these  may  vary  widely  within  the  temperature  range  to  which 
the  piece  will  be  subjected. 

151 


152  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

The  first,  second,  third,  and  fourth  are  but  elements  of  the  heating 
process,  and  the  sixth  of  the  cooling.  The  method  of  heating  the  alloy 
steels  is  very  important,  as  mechanical  injuries  are  liable  to  occur,  in 
the  external  layers  of  the  metal  as  well  as  the  internal,  from  a  too  rapid 
rise  in  the  temperature,  especially  at  the  start. 

The  highest  temperature  to  which  it  is  safe  to  submit  a  steel  for  heat- 
treating  is  governed  by  the  chemical  composition  of  the  steel,  and  this 
temperature  should  be  about  40°  F.  above  the  highest  point  of  trans- 
formation in  the  steel  considered.  This  pure  carbon  steel  should  be 
raised  to  from  1450°  to  1650°  F.,  according  to  the  carbon  content, 
while  some  of  the  high-grade  alloy  steels  may  safely  be  raised  to 
1750°  F.,  and  the  high-speed  steels  may  be  raised  to  just  below  the 
melting  point.  It  is  necessary  to  raise  the  metal  to  these  points  so  that 
the  desired  change  in  structure  will  be  secured.  If  raised  far  above  these 
temperatures  in  an  oxidizing  atmosphere,  the  surface  of  the  piece  becomes 
covered  with  a  scale  of  iron  oxide  and  oxidation  extends  to  the  elements 
combined  with  the  iron. 

When  these  oxides  remain  within  the  metal,  they  tend  to  form  a  film 
of  separation  between  the  metallic  grains,  thus  destroying  the  cohesion 
between  them,  and  the  metal  is  said  to  be  burned.  After  burning,  it 
cannot  be  brought  back  to  its  former  strength  without  remelting.  If 
the  temperature  is  maintained  within  the  crystallogenic  zone,  disaggre- 
gation  proceeds,  so  that  the  longer  it  is  subjected  to  this  temperature 
and  the  higher  the  temperature,  the  less  homogeneous  it  becomes  and 
the  coarser  its  grain  after  cooling.  Steel  in  this  state  is  called 
over-heated.  It  can  be  partially  returned  to  its  former  strength  by 
repeated  forging  when  heated  above  the  critical  temperature,  followed 
by  positive  quenching,  or  it  may  be  restored  by  a  proper  method  of 
heat-treating. 

When,  as  always  happens,  the  grain  has  become  coarsened  by  over- 
heating it  must  be  refined  again  to  bring  it  back  to  its  original  condition. 
To  do  this  it  is  necessary  to  heat  the  metal  to  the  point  where  a  .new  crys- 
tal-size is  born,  as  the  coarsening  of  the  grain  is  merely  a  growth  of  the 
crystals,  and  these  crystals  grow  with  every  increase  in  the  temperature 
above  the  point  necessary  for  hardening  or  annealing.  If  we  barely  pass 
the  degree  of  temperature  at  which  this  new  crystal-size  is  born  we  will 
obtain  the  smallest  grain  size  that  the  steel  is  capable  of.  This  tem- 
perature varies  with  the  carbon  content  of  the  steel.  The  higher  the  per- 
centage of  carbon  the  lower  the  degree  of  temperature  that  will  be  required; 
a  low-carbon  steel  must  be  heated  to  1650°  F.,  a  0.40%  carbon  steel 
to  1475°  F.,  and  so  on.  Some  of  the  special  alloying  materials  also  affect 
this  temperature  as  well  as  the  size  of  the  grain. 


FURNACES  AND  FUELS  USED  FOR  HEAT  TREATMENT         153 


FURNACES  AND  THEIR  FUELS 

Owing  to  the  nature  of  most  steels  they  must  be  handled  very  care- 
fully in  the  processes  of  annealing,  hardening,  and  tempering;  for  this 
reason  much  special  apparatus  has  been  installed  in  the  past  few  years 
to  aid  in  performing  these  operations  with  definite  results.  This  appa- 
ratus is  divided  into  two  distinct  classes;  that  is,  the  apparatus  for  heating 
the  metal,  and  that  for  cooling.  In  heating  the  metal  four  methods  are 
used;  namely,  furnaces  using  solid  fuel,  liquid  fuel,  gaseous  fuel,  and  elec- 
tricity. 

The  forge  fire  was  at  first  used  for  burning  sclid  fuels,  such  as  coal, 


FIG.    77.  —  Hard   fuel  furnace  for  heat- 
treating  steel. 

coke,  charcoal,  etc.,  to  heat  metals.  From  this  developed  the  enclosed 
furnace,  as  shown  in  Fig.  77,  and  consequently  these  are  the  most  numerous. 
In  the  furnace  is  a  grate  on  which  to  burn  the  fuel,  and  over  this  an  arch 
to  reflect  the  heat  back  to  a  plate  on  which  the  work  is  placed.  This 
plate  should  be  placed  so  that  the  flames  will  not  come  in  contact  with 
the  pieces  of  metal  to  be  heat-treated.  For  this  reason  cast  iron  or  clay 
retorts  are  sometimes  used  in,  the  furnace  to  place  the  work  in,  while  the 
necessary  heat  is  obtained  by  the  flames  encircling  these.  They  only 
have  an  opening  on  one  side,  ajid  this  is  placed  opposite  the  front  door, 
so  the  work  can  be  easily  passed  in  and  out.  The  oxidation,  sulphura- 


154  COMPOSITION    AND    HEAT-TREATMENT   OF   STEEL 

tion,  etc.,  that  spoil  the  smooth  surfaces  of  the  work,  and  are  largely 
caused  by  the  products  of  combustion  of  the  hard  fuels,  are  thus  eliminated 
as  much  as  possible  with  this  kind  of  furnace  and  fuel.  With  this  furnace 
it  is  necessary  to  keep  the  heat  in  and  the  cold  air  out  as  much  as  pos- 
sible, and  therefore  the  doors  should  open  and  close  very  quickly  to  aid 
in  the  rapid  handling  of  the  work.  For  this  reason  the  sliding  doors 
with  counterbalancing  weights,  as  shown,  should  be  used. 

The  disadvantage  of  this  style  of  furnace  is  that  it  is  almost  impos- 
sible to  keep  a  constant  temperature,  and  as  a  chimney  must  be  provided, 
much  heat  is  lost  through  that.  By  not  being  able  to  keep  a  constant 
temperature,  it  is  impossible  to  measure  the  heat  with  a  pyrometer,  and 
the  heat  must  be  judged  entirely  by  the  color,  as  seen  with  the  eye,  and 
this  makes  the  results  depend  entirely  on  the  skill  and  experience  of  the 
workman.  Also  the  atmospheric  air  or  gases  generated  by  combustion 
or  a  mixture  of  both  come  in  contact  with  the  hot  metal.  These  are 
liable  to  cause  the  metal  to  lose  some  of  its  carbon  content,  especially 
at  corners  or  on  thin  delicate  sections,  from  the  oxidizing  influence  of 
the  oxygen  in  the  air.  The  fuel  is  also  liable  to  contain  injurious  ingre- 
dients, such  as  sulphur,  which  may  enter  the  steel. 


LIQUID    FUEL 

Furnaces  that  use  a  liquid  for  fuel,  such  as  crude  oil,  kerosene,  gaso- 
lene, naphtha,  etc.,  are  becoming  more  numerous  every  day,  owing  to 
the  ease  with  which  the  fire  is  handled  and  their  cleanliness  as  compared 
with  a  coal,  coke,  or  charcoal  fire. 

Crude  oil  and  kerosene  are  the  fuels  generally  used  in  these  furnaces, 
owing  to  their  cheapness  and  the  fact  that  they  can  be  obtained  nearly 
everywhere.  The  adoption  of  oil  for  fuel  has  resulted  in  a  considerable 
saving  in  the  fuel  bill  over  that  of  the  coal-burning  furnaces,  and  has 
also  made  a  big  improvement  in  the  cleanliness  of  the  hardening  room. 
In  fact,  where  natural  gas  is  not  obtainable  at  about  one-quarter  of  the 
usual  price  of  city  gas,  crude  oil  is  by  far  the  cheapest  fuel  that  can  be 
obtained  for  heat-treating  furnaces.  An  exception  to  this  might  be  made 
in  the  future  when  considering  producer  gas,  but  at  present  enough  data 
has  not  been  obtained  by  which  to  draw  comparisons. 

One  of  the  simpler  of  these  oil-burning  furnaces  is  shown  in  Fig.  78. 
With  any  of  the  oil  furnaces  gas  can  be  used  as  a  fuel  by  merely  changing 
the  burners.  With  a  properly  designed  furnace  the  temperature  can 
be  raised  quickly  to  the  point  desired;  can  be  maintained  at  this  tem- 
perature for  any  length  of  time,  and  an  even  heat  can  be  kept  throughout 
the  entire  chamber  of  the  furnace.  With  the  proper  fuels  and  valve 
for  regulating  this,  the  temperature  in  the  furnace  can  be  raised  or 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


155 


lowered  as  rapidly  or  as  slowly  as  necessary  for  the  different  kinds  of 
work.  In  the  annealing  of  metals  also  the  rate  of  cooling  can  be  made 
as  slow  as  needed  if  the  proper  equipment  is  installed.  All  of  this  can 
be  accomplished  without  the  customary  smoke,  soot,  ashes,  dust,  gases, 
and  foul  odors  that  are  met  with  in  hardening  rooms  where  the  old  hard 
fuel  furnaces  are  used.  The  saving  in  the  time  consumed  by  the  oper- 
ator in  running  the  furnace  is  also  an  important  factor,  as  when  the  proper 
temperature  is  once  obtained  and  the  valves  set,  practically  no  time  is 
required  for  this  part  of  the  work. 

The  installation  of  the  furnaces  and  their  necessary  equipment  is  very 
important  for  the  proper  operation  of  the  same.  For  safety,  it  is  best 
to  have  the  fuel  supply  in  a  tank  outside  of  the  building  and  pipe  it,  under- 


Fic.78.  —  Oil-burning,  annealing,  tempering, 
and  hardening  furnace. 

neath  the  floor,  to  the  furnace.  As  a  blast  of  air  is  necessary,  this  can 
also  be  piped,  under  the  floor,  from  the  fan,  blower,  or  air  compressor. 
The  air  and  fuel  pressures  must  be  steady  and  uniform,  and  there  must  be 
volume  enough  to  give  the  furnaces  their  proper  temperature  and  main- 
tain it  at  the  point  desired.  This,  of  course,  varies  with  the  kinds  of 
material  to  be  heated.  . 

Where  accurate  temperature  control  is  not  necessary,  and  pressure 
under  14  ounces  will  suffice,  a  steel  fan  or  pressure  blower,  that  will  give 
the  proper  volume,  will  do  the  work.  Where  pressures  from  2  to  5  pounds 
are  required  the  positive  pressure  blower  is  needed,  and  when  an  air 
pressure  above  this  is  necessary  a  compressed-air  plant  will  be  needed. 
In  some  cases  good  dry  steam  will  give  better  results  at  a  high  pressure 
and  effect  a  saving  in  the  fuel.  In  that  case  steam  pipes  take  the  place 


156 


COMPOSITION    AND    HEAT-TREATMENT   OF    STEEL 


of  the  air  pipes,  and  these  connect  up  to  the  steam  supply.  The  quantity 
of  fuel  needed  varies  with  the  temperature  required,  material  treated, 
and  speed  at  which  it  is  handled,  but  the  fuel  pressure  must  always  be 
uniform.  For  the  oil  5  pounds  pressure  is  sufficient. 


FIG.  79.  —  High-pressure  oil  burner. 

In  some  cases  between  the  tank  and  furnace  is  located  a  coil  of  pipe 
through  which  the  fuel  flows  and  over  which  a  stream  of  water  is  flowing 
to  keep  the  liquid  at  a  low,  even  temperature  when  it  enters  the  burners, 
which  are  located  in  the  furnace. 

The  burner  to  be  used  is  an  important  factor  in  economical  produc- 
tion, and  it  is  not  practica1  to  have  one  burner  that  will  do  all  kinds  of 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT         157 

work.  Whether  high  or  low  pressure  air  or  steam  is  to  be  used  for  the 
blast  makes  a  difference  in  the  kind  of  burner  that  should  be  used  to 
get  the  greatest  efficiency  with  the  minimum  fuel  consumption,  as  well 
as  the  temperature  that  it  is  necessary  to  maintain  in  the  forge,  and  the 
nature  of  the  work  that  is  to  be  done.  In  Fig.  79  is  shown  a  good  design 
of  high-pressure  oil  burner. 


.C.L.BU 


C.L.Burner    - 


FIG.  80.  —  Details  of  construction  of 
over-fired  furnaces. 


The  dial  with  the  figures  and  the  pointer  at  the  bottom  have  been 
added  for  fine  adjustment.  The  sectional  view  at  the  tip  shows  the  method 
of  controlling  the  volume  of  atomized  oil  that  is  injected  into  the  furnace. 

With  this  fuel  hardly  any  work  is  required  to  keep  up  the  fires,  as  they 
can  be  lighted  in  the  morning  and  the  temperature  regulated  by  the  turn- 
ing of  a  few  valves  and  cocks.  A  more  even  temperature  can  thus  be 


158 


COMPOSITION    AND    HEAT-TREATMENT    OF   STEEL 


kept  in  the  furnace  than  with  the  solid  fuels,  but  the  opening  of  the  doors 
to  handle  the  work  reduces  the  temperature  of  the  furnace  the  same  as 
with  the  solid  fuels.  The  action  of  the  gases  of  combustion  or  the 
oxygen  of  the  atmosphere  in  attacking  the  hot  metal  gives  the  same 
disadvantages. 

The  furnaces  are  built  in  the  over-fired  and  the  under-fired  type. 
In  the  over-fired  furnace,  as  shown  in  Figs.  80  and  81,  the  atomized  gas 
from  the  oil  burner  is  sent  into  an  opening  over  the  heating  chamber 
that  is  separated  from  it  by  an  arch.  Here  the  gas  is  burned  and  passes 


FIG.  81.  —  Small  over-fired  furnace. 

through  numerous  openings  in  the  arched  roof  of  the  heating  chamber, 
as  indicated  by  the  arrows  in  the  right-hand  view  in  Fig.  80.  The  burned 
gases  then  pass  out  through  holes  in  the  side  of  the  heating  chamber,  close 
to  its  floor;  then  under  it  and  up  through  flues  on  the  opposite  side. 

Thus  the  entire  heating  chamber  is  uniformly  filled  with  the  products 
of  combustion  and  the  spent  gases  utilized  to  heat  the  floor  of  the  working 
chamber.  This  gives  a  soft  uniform  heat  throughout  the  working  cham- 
ber, and  the  temperature  is  so  easily  raised,  lowered,  and  controlled  that 
overheating  or  burning  the  metal  can  only  result  from  gross  carelessness. 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


159 


This  uniform  heat  in  the  heating  chamber  also  reduces  to  a  minimum 
the  distortion  and  warping  that  results  from  uneven  heating,  and  a  more 
even  hardness  can  be  obtained  throughout  the  piece  than  can  be  produced 
with  a  hard  fuel  or  under-fired  furnace. 

With  the  proper  fuel  supply  and  valves  to  control  the  same,  the  tem- 
perature of  the  heating  chamber  can  be  maintained  for  an  indefinite 
period,  within  25°  F.  of  any  temperature  between  600°  and  2000°  F. 


FIG.  82.  —  Double-end  furnace  with  tank  for  quenching  bath  attached. 

On  test  runs  of  l£  hours  each,  at  certain  temperatures,  the  variation  was 
not  over  10  degrees. 

For  high-grade  alloy  steels,  where  the  most  accurate  results  are  required, 
the  muffle  furnace  should  be  used,  in  order  to  avoid  the  action  of  the  prod- 
ucts of  combustion  on  the  metal,  since  it  is  liable  to  absorb  some  impu- 
rities from  the  gases.  These  impurities  might  weaken  the  metal  and  leave 
it  less  able  to  withstand  the  strains  and  stresses  put  upon  it  than  would 
be  the  case  if  the  metal  were  protected  from  them.  For  ordinary  work, 


160 


COMPOSITION    AND    HEAT-TREATMENT   OF   STEEL 


however,  the  injury  is  so  slight  it  can  be  overlooked,  and  the  fuel  consump- 
tion is  much  lower  in  the  oven  than  in  the  muffle  furnace. 

A  furnace  open  at  both  ends,  wth  a  tank  attached  to  hold  the  quench- 
ing bath,  is  shown  in  Fig.  82. 


ra  ra  f 

"I  !        ! 


Longitudinal  Section. 


Cross  Section  A-B. 


FIG.  83.  —  Details  of  under-fired  furnace. 

In  the  under-fired  furnace,  as  shown  in  Figs.  83  and  84,  atomized  gas 
is  injected  into  an  opening  underneath  the  heating  chamber,  and  there 
the  combustion  takes  place.  It  then  passes  through  flues  into  the  top 
of  the  heating  chamber,  and  out  of  here  through  openings  near  the  floor 


FURNACES    AND  FUELS    USED    FOR    HEAT-TREATMENT         161 

into  flues  on  the  opposite  side.  These  conduct  it  out  of  the  furnace. 
The  burners  and  the  flues  on  this,  as  well  as  the  over-fired  furnace,  are 
staggered  on  opposite  sides  of  all  the  larger  furnaces,  to  make  the  heat 
uniform  in  all  parts  of  the  heating  chamber. 

The  construction  of  this  furnace  is  simpler,  and  hence  its  first  cost 
is  less  than  that  of  the  over-fired  type.  It  is  also  much  easier  to  reline 
arid  repair  when  burned  out.  The  fuel  consumption,  however,  is  slightly 
greater  than  in  the  over-fired  type  and  a  uniform  heat  in  all  parts  of  the 


FIG.    84.  —  Small  under-fired    furnace    with    complete 
oil-burning  outfit. 

work  chamber  is  not  as  easily  obtained,  especially  in  large  furnaces.  In 
the  smaller  under-fired  furnaces  the  heat  is  easily  controlled,  and  with 
oil  fuel  a  high  temperature  can  be  attained  and  maintained  throughout 
the  day.  This  makes  it  very  useful  for  tool  hardening  and  tempering. 

In  Fig.  85  is  shown  an  oil-burning  furnace  with  a  self-contained  outfit 
that  makes  it  portable,  and  Fig.  86  shows  one  with  a  water-cooled  front. 
The  latter  is  made  of  fire-brick,  with  any  size  or  shape  of  openings  desired, 
and  is  very  useful  for  heating  the  ends  of  tools  and  keeping  the  bar  cool 
enough  to  handle.  In  both  of  these  furnaces  a  temperature  of  2500°  F.  can 
easily  be  maintained,  and  thus  any  kind  of  high-speed  steel  can  be  hardened. 


162 


COMPOSITION   AND   HEAT-TREATMENT  OF   STEEL 


Another  style  of  oil  furnace  is  the  muffle  furnace.  In  this  the  gases 
surround  the  heating  chamber,  but  do  not  enter  it.  Thus  the  metal  is 
protected  from  any  injurious  effects  from  the  gases  of  combustion  while 
they  are  being  heated. 

Any  of  the  above  liquid  fuel  furnaces  can  be  used  for  the  gaseous 
fuels  by  merely  changing  the  burners. 


Fia.  85.  —  Portable  oil  furnace  with  self-contained 
outfit. 


GASEOUS    FUEL 

Furnaces  using  gaseous  fuel  are  growing  in  favor,  and  are  constructed 
so  they  can  use  either  natural  gas,  artificial  gas,  or  producer  gas.  They 
are  very  easy  to  regulate,  and  if  well  built  are  capable  of  maintaining  a 
constant  temperature  within  a  wide  range.  Their  first  cost  is  greater 
than  that  of  solid  fuel  furnaces.  The  cost  of  installation,  however,  is  soon 
paid  for  where  natural  gas,  or  possibly  producer  gas,  is  used  for  fuel,  as 
then  it  is  the  cheapest  furnace  to  operate.  Artificial  or  city  gas  is  more 
expensive  than  oil  for  fuel,  but  is  much  cleaner  and  easier  to  operate,  as 
it  is  not  necessary  to  install  tanks  or  apparatus  in  which  to  store  the  supply. 
If  the  cost  of  the  upkeep  of  these  be  figured  in,  there  might  not  be  such 
a  great  difference  in  the  cost  of  furnace  fuel,  providing  the  city  gas  be 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT         163 

obtained  at  a  reasonable  price.     Where  high-grade  steels  are  used,  and  the 
best  work  is  demanded,  doubtless  gas  is  the  best  fuel. 

Producer  gas  is  continually  increasing  in  use  for  furnaces,  but  unless 
a  number  of  furnaces  are  operated,  or  a  few  large  ones,  a  separate  pro- 
ducer plant  to  supply  the  furnaces  is  not  economical.  Where  a  producer 
plant  can  be  utilized  for  other  things,  such  as  furnishing  power,  it  is  prob- 
ably a  very  cheap  fuel  to  pipe  from  the  central  power  plant  and  burn 
in  the  furnaces.  With  this,  or  any  of  the  gas  fuels,  a  large  part  of  the 
heat  that  goes  up  the  chimney,  when  other  fuels  are  used,  can  be  utilized 
in  heating  the  air  of  combustion  that  enters  the  furnace.  This  can  be 
done  with  very  little  special  construction. 


Fig.  86.  —  Oil  furnace  with  water  jacketed  front. 

Results  which  are  very  uniform  are  obtained  with  the  gas  furnaces, 
and  it  is  much  easier  to  maintain  a  constant  temperature  for  liquid 
baths  than  in  a  solid  fuel  furnace,  or  a  metal  retort  may  be  used 
to  place  the  work  in  for  the  purpose  of  keeping  it  away  from  the  gases 
of  combustion,  with  a  greater  assurance  that  the  work  in  it  will  be 
raised  to  the  proper  temperature  and  maintained  evenly  for  a  given 
length  of  time. 

One  of  the  muffle  or  oven  style  of  furnaces  that  uses  gas  for  fuel  is 
shown  in  Fig.  87.  In  this  the  blast  connects  at  C  with  the  end  of  the 
drum  D,  and  goes  through  the  pipe  A,  where  it  picks  up  the  gas  at  G 
and  carries  it  to  the  burners  B.  In  placing  a  cutter  like  X,  in  the  furnace, 
it  should  be  supported  by  a  fire-brick  similar  to  F,  so  the  teeth  will  not 
touch  the  bottom  slab  Z.  The  door  E  has  a  counterweight  above  H, 


164 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


so  it  can  be  opened  and  closed  quickly,  and  it  slides  in  the  guides  S.  At 
P  is  a  peep-hole,  and  at  V  is  a  vent  to  allow  the  gases  to  escape  from  the 
furnace.  This  principle  has  been  carried  farther  by  revolving  the  oven, 


FIG.  87.  —  Gas  furnace  with  oven. 

or  work  holder,  and  sending  the  heating  gases  around  it,  as  shown  in 
Fig.  88. 

Pyrometers  can  be  used  very  easily  to  measure  the  heat  with  this 
style  of  furnace.  Thus  definite  results  may  be  obtained  in  the  degree 
of  temperature  without  depending  on  the  skill  or  knowledge  of  the  work- 


FURNACES   AND    FUELS    USED    FOR    HEAT-TREA'AlENT         165 

man  to  as  great  an  extent  as  with  the  furnaces  using  coal,  coke,  or  charcoal 
for  fuel.  Furnaces  using  liquid  and  gaseous  fuels  differ  very  little  in 
their  construction,  and  are  made  in  many  different  styles  and  sizes  to  suit 
the  various  materials  they  are  to  handle,  or  the  kind  of  heat-treatment. 

An  instance  of  this  is  shown  by  the  upright  furnace  in  Fig.  89,  which 
is  for  heating  long  bars  or  steel  pieces.  The  heat  is  evenly  distributed 
in  the  heating  chamber  by  regulating  burners  F,  which  enter  the  furnace 
from  four  sides  and  on  a  tangent,  so  as  to  give  the  flames  a  swirling  motion. 
They  are  controlled  by  the  gas  and  air  valves,  A  and  G.  For  short  lengths 
the  upper  burners  E  are  shut  off,  and  the  section  Y  can  be  removed  and 


FIG.  88.  —  Gas  furnace  with  revolving  retort. 

cover  Z  lowered.  The  large  opening  at  /  will  give  the  necessary  draft, 
and  vents  H  can  be  used  for  peep-holes,  while  vent  P  allows  the  used 
gases  to  escape. 

Special  designs  of  furnaces  have  been  made  for  all  of  the  various  oper- 
ations of  heat-treating,  such  as  annealing,  tempering,  hardening,  coloring, 
etc.  Some  of  these  have  been  made  continuous  operating  and  automatic 
as  shown  in  Figs.  90  to  93  inclusive.  In  Figs.  90  and  91  is  shown  the  fur- 
nace combined  with  a  quenching  bath,  into  which  the  work  drops  directly 
from  the  furnace.  This  quenching  tank  contains  an  automatic  conveyer 
that  lifts  the  work  out  of  the  tank  and  dumps  it  into  a  wheelbarrow  shown 


166  COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 

in  Fig.  91.  Fig.  91  shows  the  details  of  the  furnace  as  supplied  with  a 
smooth  lining,  and  Fig.  92  shows  the  helical  or  worm  lining  that  can  be 
used  with  the  same  furnace  if  desired.  The  furnace  is  mounted  in  such 
a  manner  that  its  axis  may  be  tilted  at  an  angle,  giving  the  revolving 
hearth  an  incline,  with  the  discharge  end  lower  than  the  entrance  or  feed 
end.  The  gradual  incline  causes  the  material  to  feed  forward,  and  by 
means  of  a  hand- wheel  the  degree  of  pitch  may  be  adjusted  so  as  to  regu- 


FIG.  89.  —  Upright  gas  furnace. 

late  the  progression  of  the  material  through  the  furnace,  and  consequently 
the  time  of  heating. 

The  advantages  of  this  method  of  automatic  continuous  heating  are 
many:  The  material  is  charged  in  a  hopper  in  bulk  at  one  end  of  the  fur- 
nace and  fed  automatically  into  the  chamber.  It  comes  continually 
in  contact  with  the  newly  heated  interior  surface,  which  is  revolving, 
thereby  absorbing  the  heat  from  the  lining  as  well  as  from  the  heated 
gases.  In  a  stationary  furnace  the  heat  from  the  sides  and  roof  are  not 
utilized,  as  the  material  remains  in  a  fixed  position;  that  farthest  removed 
from  the  heat  requires  a  much  longer  period  to  be  brought  to  the  desired 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


167 


temperature  and  the  more  exposed  pieces  are  liable  to  overheating,  while 
others  are  insufficiently  heated.     To  prevent  oxidation,  the  end  of  the 


FIG.  90.  —  Automatic  and  continuous  hardening  furnace,  with  tilting  mechanism. 

discharge  spout  may  be  carried  beneath  the  level  of  the  bath,  thereby 
sealing  it  and  excluding  the  air. 

In  operation,  the  pieces  are  fed  continuously  into  one  end  of  the  cylin- 


FIG.  91.  —  Details  of  continous  hardening  furnace,  showing  smooth  interior. 

der.  The  furnace  is  fired  internally  from  the  opposite  end,  with  the  zone 
of  highest  temperature  at  the  discharge  end.  The  cylinder  revolves 
slowly  (1  to  4  revolutions  per  minute),  and  owing  to  the  slight  inclina- 


168 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL" 


tion  of  the  furnace,  the  pieces  treated  fall  slightly  forward  at  each  revo- 
lution, gradually  progressing  toward  the  discharge  end,  where  they  enter 
a  proper  receptacle  or  bath  upon  reaching  the  desired  temperature. 

In  certain  classes  of  work,  such  as  balls,  nuts,  and  uniform  shapes, 
the  helical  or  worm  type,  as  shown  in  Figs.  92  and  93,  is  used,  but  for 
irregular  shapes,  where  the  smooth  lining  can  be  used,  the  cost  is  less 
and  a  greater  life  is  insured.  Fig.  93  shows  the  details  of  construction 


FIG.  92.  —  Section  of  same  furnace  with 
helical  or  worm  interior. 

of  a  furnace  built  on  the  same  principle,  with  the  exception  that  the  work 
is  held  in  a  revolving  retort,  and  the  heating  gases  surround  this  in  such 
a  way  that  they  do  not  come  in  contact  with  the  work. 

Oil  or  gas  fuel  may  be  used  and  perfectly  uniform  results  obtained, 
as  the  work  treated  is  heated  gradually  with  every  portion  of  its  surface 
exposed  to  the  direct  action  of  the  hot  gases  and  lining,  and  both  tem- 


FIG.  93.  —  Sectional  view  of  furnace  with 
closed  retort  for  work. 

perature  and  time  are  maintained  constant.  The  furnaces  are  built 
to  suit  a  wide  range  of  requirements,  and  in  sizes  that  will  handle  up  to 
2000  pounds  of  stock  per  hour.  While  they  were  designed  principally 
for  hardening  steel  pieces,  they  are  also  useful  for  annealing  non-ferrous 
metals,  such  as  brass  cartridge  shells,  etc. 

Automatic  apparatus  has  also  been  added  to  furnaces  to  carry  the 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


169 


work  through  quenching  and  cleansing  baths  of  various  kinds.  In  one 
case  an  automatic  gas-heating  furnace  discharges  its  work  into  a  tank 
for  quenching.  The  quenching  tank  contains  a  conveyer  for  removing 
it  from  the  tank  into  receptacles  with  which  it  can  be  carried  away. 
Two  tanks  can  also  be  coupled  together;  into  the  first  one  of  which  the 
work  is  dumped  from  the  furnace  for  quenching.  From  there  it  is  con- 
veyed to  the  second  tank,  in  which  the  work  is  cleaned,  and  from  there 
conveyed  to  pans,  trays,  or  other  containers  in  which  it  can  be  easily 
handled.  The  work  drops  from  the  furnace  into  the  quenching  bath 
in  a  continuous  stream,  and  from  the  hopper  it  is  fed  through  a  perforated 


FIG.    94.  —  Gas   booster   to    supply 
furnaces. 

barrel,  that  inclines  down  to  the  other  end  of  the  tank,  where  it  is  picked 
up  by  the  conveyer  and  discharged  from  the  tank.  The  perforated  barrel 
revolves  slowly  to  agitate  the  articles,  thus  bringing  them  in  contact 
with  the  quenching  liquid  on  all  sides.  The  barrel  end  next  to  the  hopper 
is  movable,  so  it  can  be  raised  or  lowered  to  make  the  work  travel  fast 
or  slow.  The  liquid  is  admitted  to  the  tank  beneath  the  receiving  end 
of  the  barrel,  and  as  it  becomes  heated,  by  contact  with  the  articles,  it 
rises  and  is  drained  off,  from  the  top  of  the  tank,  near  the  discharge  end 
of  the  barrel.  At  the  lower  end  of  the  barrel  the  pieces  are  picked  up 
by  the  lower  loops  of  an  endless  chain  that  is  formed  of  buckets  open  on 
the  inner  side.  They  are  elevated  by  this  and  dumped  into  a  fixed  hop- 
per within  the  upper  loop  of  the  chain,  and  from  there  the  discharge  chute 


170  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

leads  them  away  from  the  tank.  The  buckets  are  perforated  so  as  to 
strain  the  liquid  from  the  pieces  hardened. 

The  double  tanks  may  be  used  to  quench  work  in  the  one,  and  then 
send  it  through  a  cleaning  compound  in  the  other.  For  instance,  work 
that  is  quenched  in  oil  may  be  sent  through  a  second  tank  containing 
some  liquid  that  will  cut  the  oil  from  the  work  and  leave  it  clean,  or  a 
liquid  containing  chemicals  that  act  as  a  rust  preventative  may  be  used 
in  the  second  tank.  In  fact  there  are  many  combinations  for  the  double 
tank. 

The  gas  pipes  from  the  street  or  the  main  in  the  street  are  sometimes 
found  to  be  too  small  to  supply  the  necessary  gas  to  the  furnaces  when 
installing  them.  In  this  case  a  gas  booster,  similar  to  that  shown  in  Fig. 
94,  is  used.  This  sucks  the  gas  from  the  main  faster  than  it  would  natu- 
rally flow,  and  delivers  it  to  the  furnaces  as  required. 

With  gaseous  fuels,  it  is  probably  as  easy  to  control  the  temperature 
of  furnaces  to  within  a  few  degrees  of  a  given  point  as  with  any  fuel 
used.  The  latest  invention  along  this  line  is  the  automatic  apparatus, 
for  controlling  the  temperature  of  gas  furnaces.  It  was  put  on  the  market 
by  the  American  Gas  Furnace  Company  in  December,  1909,  and  controls 
the  temperature  to  within  5  degrees  of  a  given  point.  Pyrometers  being 
required  to  measure  these  high  heats,  the  pointer  on  the  pyrometer  indi- 
cator was  used  as  a  starting  point.  The  pointer  was  left  free  to  oscillate 
back  and  forth  as  the  temperature  rises  or  falls  in  the  furnace,  as  any- 
thing that  would  retard  the  action  of  this  pointer  would  throw  the 
pyrometer  out  of  true  and  ruin  it  for  accurate  temperature  readings.  At 
•the  same  time  it  was  necessary  to  have  power  enough  to  instantaneously 
open  and  close  the  gas  and  air  valves  that  admit  the  fuel  to  the  furnace. 
The  mechanism  also  had  to  be  positive  in  its  action. 

In  Fig.  95  is  shown  a  muffle  gas  furnace  with  the  complete  automatic 
temperature  controlling  apparatus  attached  thereto;  Fig.  96  shows,  on 
a  much  larger  scale,  the  apparatus  connected  to  the  indicator;  Figs.  97 
and  98  show  the  operating  mechanism  of  the  apparatus  connected  to 
the  indicator,  and  Fig.  99  shows  the  apparatus  connected  to  the  furnace. 
The  instrument  operates  as  follows: 

In  Fig.  95  the  thermo-couple  or  hot  end  of  the  pyrometer  is  inserted 
into  the  furnace  at  A,  and  connected  to  the  indicator  at  B.  Underneath 
B  is  the  mechanism  shown  in  Fig.  96,  while  at  C  is  that  shown  in  Fig.  99. 
At  D,  in  Fig.  96,  is  located  a  thumb  screw  that  revolves  the  disk  E  and 
moves  the  pointer  F  with  its  arms,  G,  to  the  temperature  at  which  it  is 
desired  to  maintain  the  furnace.  The  arms  G,  as  well  as  the  rest  of  the 
mechanism,  are  operated  by  power  supplied  from  a  fan  located  in  the 
case  J.  This  is  revolved  by  a  current  of  air  that  is  sent  through  a  J-inch 
pipe,  and  blows  against  the  blades  of  the  fan. 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


171 


How  the  arms  G  operate  is  best  shown  by  the  drawing,  Fig.  97,  which 
is  a  view  that  looks  down  on  their  top.  When  the  temperature  rises  in 
the  furnace,  the  indicator  pointer  /  travels  to  the  right  until  it  passes 
under  the  left-hand  arm  G,  which  is  now  stationary,  and  comes  in  contact 
with  the  right-hand  arm  (7,  which  is  constantly  oscillating  in  and  out  of 


FIG.  95.  —  Instrument  for  automatically  controlling  temperature  of  furnaces. 

slot  H.  When  it  arrives  at  the  position  shown,  right-hand  arm  G  grips 
it  for  an  instant,  and  this  trips  the  arm  and  throws  it  back  to  the  posi- 
tion shown  by  left-hand  arm  G,  so  that  the  indicator  pointer  /  will  pass 
it  and  register  any  rise  in  temperature  which  may  occur  after  this,  due 
to  the  lag.  When  right-hand  arm  G  is  thrown  back  to  the  stationary 


172 


COMPOSITION   AND   HEAT-TREATMENT  OF  STEEL 


position,  left-hand  arm  G  is  started  oscillating  in  and  out  of  slot  H,  by 
means  of  a  cam.  The  valves  that  admit  the  gas  and  air  into  the  furnace 
for  fuel  are  then  shut  off,  thereby  stopping  the  heat.  Then  as  the  fur- 
nace cools  and  the  indicator  pointer  /  travels  back  to  the  left  to  record 
the  lowering  temperature,  left-hand  arm  G  catches  it,  trips,  turns  on  the 
gas  and  air,  and  the  right-hand  arm  G  starts  operating. 


FIG.  98.  —  Apparatus  connected  to  the  indicator. 

The  arms  G  are  given  their  oscillating  motion  or  held  stationary  by 
the  lower  end  riding  on  two  disks  K,  that  alternately  act  as  cams  and  are 
fastened  together,  as  shown  in  Figs.  96  and  98.  The  disks  K  are  moved 
back  and  forth  on  their  centers' by  piece  L,  which  is  moved  back  and  forth 
the  distance  of  the  opening  M.  Piece  L  rides  on  bar  N  for  one-half  of 
this  distance,  and  for  the  other  half,  the  half  round  in  the  top  in  the  open- 
ing M  drops  over  the  bar  N  and  moves  it  back  and  forth  to  oscillate  the 
disks  K.  While  doing  so,  the  end  of  bar  N  rides  on  a  flat  spot  in  the  valve 
rod  0,  but  when  one  of  the  arms  G  is  tripped  and  the  other  starts  oper- 


FURNACES    AND    FUELS    USED    FOR   HEAT-TREATMENT        173 

ating,  the  end  of  bar  N  pushes  in  or  out  the  valve  end  0,  and  opens  or 
closes  an  air  valve  that  sends  a  current  of  air  into  a  diaphragm  that  is 
located  in  the  lower  part  of  the  apparatus  shown  in  Fig.  99.  As  will 
be  seen  in  Fig.  98,  one  of  the  G  arms  is  riding  on  the  cam  of  the  disk  K 
and  is  therefore  in  motion,  while  the  other  G  arm  is  riding  on  the  outer 
circle  and  is  therefore  stationary. 

In  the  lower  part  of  the  apparatus  two  square  holes  are  provided  in 
the  cylinder  P,  Fig.  95,  to  act  as  openings  for  the  air  and  gas  to  pass  through, 
and  over  these  is  a  plate  that  raises  and  lowers  te  open  and  close  them. 
The  amount  that  these  can  be  opened  and  closed  is  regulated  by  moving 
the  arms  R  and  S,  in  Fig.  99.  These  move  the  center  rings  up  or  down 
on  the  screw,  and  they  can  be  clamped  to  it  by  the  set  screws  back  of  the 


Eig.  97 


FIGS.  97  and  98.  —  Operating  mechanism  connected  to  indicator. 

arms,  when  the  proper  amount  of  motion  for  the  valve  slide  is  decided 
upon.  The  pin  T  is  connected  to  the  slide  and  allows  it  to  be  moved 
from  the  top  to  the  bottom  ring  by  the  air  that  is  admitted  to  or  shut 
off  from  the  diaphragm  through  the  pipe  U. 

One  point  on  the  arbitrary  scale  on  the  disk  S  means  a  motion  of  •& 
of  an  inch  for  the  valve  slide,  and  when  the  arm  R  is  placed  at  the  "open" 
mark,  and  the  arm  S  at  the  "shut"  mark,  the  air  and  gas  passages  can 
be  opened  or  closed  by  the  slides  traveling  their  full  distance.  This  is 
seldom  done,  however,  as  the  furnace  can  usually  be  regulated  by  turning 
on  or  shutting  off  a  part  of  the  heat. 

This  apparatus  promises  to  fill  a  long-felt  want  in  furnaces  for  heat- 
treating  metals,  as  any  one  who  operates  them  knows  how  difficult  it  is 
to  keep  the  temperature  at  a  certain  given  point  by  hand-operated  valves. 


174 


COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


HEATING   IN   LIQUIDS 


Furnaces  using  liquid  for  heating  consist  of  a  receptacle  to  hold  the 
liquid,  and  a  chamber  underneath  and  around  its  sides  that  is  heated 
by  coal,  oil,  gas,  or  electricity;  the  liquid  being  kept  at  the  highest  tem- 


FIG.  99.  —  Apparatus  connected  to  the  furnace. 

perature  to  which  the  piece  should  be  heated.  The  piece  should  be  heated 
slowly  in  an  ordinary  furnace  to  about  800°  F.,  after  which  it  should  be 
immersed  in  the  liquid  bath  and  kept  there  long  enough  to  attain  the 
temperature  of  the  bath  and  then  removed  to  be  annealed  or  hardened. 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


175 


The  bath  usually  consists  of  lead,  although  antimony,  cyanide  of 
potassium,  chloride  of  barium,  a  mixture  of  chloride  of  barium  and  chloride 
of  potassium  in  different  proportions,  mercury,  common  salt,  and  metallic 
salts  have  been  used  successfully. 

This  method  gives  good  results,  as  no  portion  of  the  piece  to  be  treated 
can  reach  a  temperature  above  that  of  the  liquid  bath ;  a  pyrometer  attach- 
ment will  indicate  exactly  when  the  piece  has  arrived  at  that  temperature, 


FIG.  100.  —  Oil  or  gas  lead  (or  oil)  bath  furnace. 

and  its  surface  cannot  be  acted  upon  chemically.  The  bath  can  be  main- 
tained easily  at  the  proper  temperature,  and  the  entire  process  is  under 
perfect  control. 

When  lead  is  used  it  is  liable  to  stick  to  the  steel  and  retard  the  cool- 
ing of  the  spots  where  it  adheres.  This  can  be  overcome  to  a  large  extent 
by  using  a  wire  brush  to  clean  the  work  with.  A  better  method,  however, 
is  to  heat  the  piece  to  a  blue  color,  which  is  about  600°  F.,  then  dip  it 


176 


COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 


quickly  in  a  strong  salt  water,  and  then  heat  it  in  the  lead  bath  to  the 
hardening  temperature.  By  dipping  in  and  out  of  the  brine  quickly 
the  piece  is  completely  coated  with  salt  and  this  prevents  the  lead  from 
sticking  to  the  piece  when  heating  it  for  hardening. 

The  greatest  objection  to  the  lead  bath  is  that  impurities  such  as 
sulphur,  etc.,  are  liable  to  be  absorbed  by  the  steel,  and  thus  alter  its 
chemical  composition.  This  is  especially  so  if  the  lead  bath  is  used  for 
the  hardening  heats,  as  at  these  high  temperatures  steel  has  a  great  affinity 
for  certain  impurities.  A  notable  example  of  this  is  its  greatly  increased 
attraction  for  oxygen,  which  the  metal  absorbs  and  retains  as  oxides 


FIG.  101.  —  Lead  bath  furnace  with  hood. 

and  occluded  gases.  With  high  temperatures  lead  and  cyanide  of  potas- 
sium throw  off  poisonous  vapors  which  make  them  prohibitive,  and  even 
at  comparatively  low  temperatures  these  vapors  are  detrimental  to  the 
health  of  the  workmen  in  the  hardening  room.  The  metallic  salts,  how- 
ever, do  not  give  off  these  posionous  vapors,  hence  are  much  better  to 
use  for  this  purpose;  but  in  many  cases  the  fumes  are  unbearable. 

When  the  lead  bath  is  only  used  for  the  lower  tempering  heats  the 
furnace  shown  in  Fig.  100  is  a  good  design.  It  can  use  either  gas  or  oil 
for  fuel,  and  is  supplied  with  a  high-temperature  thermometer  to  measure 
the  heat  of  the  bath.  This  should  never  be  higher  than  is  desired  for 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT 


177 


drawing  the  temper.  It  is  a  great  improvement,  even  with  this  furnace, 
to  place  a  hood  over  it  that  is  piped  to  the  outside  of  the  building,  and 
has  a  good  draft,  to  carry  away  any  fumes  that  may  arise  from  the  bath. 
This  is  an  absolute  necessity,  however,  when  the  lead  bath  is  used  for  the 
hardening  heats,  and  for  that  reason  a  furnace,  with  its  own  hood,  similar 
to  that  shown  in  Fig.  101,  is  much  better.  These  of  course  can  be  obtained 
or  made  with  any  size  or  shape  of  lead  pot  that  is  required  for  the  work 
to  be  heat-treated. 

Cyanide  of  potassium  when  applied  to  steel  that  has  been  heated  to 


FIG.  102.  —  Gas  furnace  for  pot  of 

cyanide.  % 

a  red  heat  reduces  the  oxides  and  causes  any  scale  that  may  have  formed 
on  the  metal  to  peel  off.  Thus  soft  spots  that  may  be  caused  by  scale 
or  blisters  when  hardening  steel  can  be  abolished  by  dusting  cyanide 
on  the  piece  before  quenching  it.  It,  however,  has  another  use  in  heat- 
treating  steel,  as  when  the  metal  is  heated  to  a  red  heat,  in  a  cyanide  bath, 
it  is  slightly  carbonized  on  the  surface  and  is  thus  used  quite  extensively 
for  case-hardening.  It  should  be  kept  at  the  boiling  point  and  the  metal 
submerged  in  it  for  about  5  minutes  and  then  quenched.  This  has  resulted 
in  the  building  of  a  special  furnace  "for  heating  cyanide,  as  shown  in  Fig. 


178  COMPOSITION    AND    HEAT-TREATMENT   OF    STEEL 

102.  Here  the  cyanide  pot  P  is  suspended  by  its  flange  over  a  chamber 
filled  with  gas  flames,  and  hood  H  gathers  the  flames  and  carries  them 
out  through  pipe  S. 

Molten  cyanide  sputters  and  drops  fly,  like  red-hot  bullets,  and  conse- 
quently many  bad  burns  are  caused  by  its  use.  The  fumes  arising  from 
the  pot  are  also  very  poisonous,  and  the  cyanide  of  potassium  itself  is  a 
rank  poison.  It  is  therefore  a  dangerous  product  to  use.  Tools  dipped 
in  powdered  cyanide  and  quenched  in  a  bath  causes  the  bath  to  become 
very  poisonous,  and  the  hand  should  never  be  put  in  the  bath  to  take 
pieces  out,  as  running  sores  that  are  hard  to  heal  may  be  the  result.  Cya- 
nide is  also  injurious  to  high-carbon  or  high-speed  steels,  and  as  there  are 
many  other  chemicals  coming  into  use  that  will  do  everything  that  cya- 
nide will  do,  and  some  things  that  it  will  not  do,  this  material  is  fast  going 
out  of  use  in  heat-treating  steel.  The  metallic  salts  are  taking  its  place 
and  doing  much  better  work,  and  they  are  not  poisonous. 

A  barium-chloride  bath  offers  all  the  advantages  obtained  from  a  lead 
bath,  or  cyanide,  and  to  this  is  added  the  advantage  of  the  barium  chloride 
forming  a  coating  on  the  steel  while  it  is  being  transferred  from  the  heat- 
ing bath  to  the  quenching  bath.  This  prevents  the  metal  from  becoming 
oxidized,  by  keeping  it  from  coming  in  contact  with  the  oxygen  in  the 
air.  It  also  volatilizes  at  a  much  higher  temperature  than  lead,  or  any 
of  the  other  materials,  used  for  heating  baths,  and  therefore  is  success- 
fully used  for  the  high  temperatures  that  are  needed  to  harden  high- 
speed steeels. 

As  pieces  heated  in  this  bath  have  the  temperature  raised  evenly, 
and  at  the  same  time,  on  all  sides  or  exposed  parts,  it  overcomes,  to  a 
very  great  extent,  the  tendency  to  warping  or  distortion  which  all  steels 
have. 

While  barium  chloride  forms  a  coating  on  the  steel  heated  in  it,  this 
coating  usually  peels  off  when  suddenly  cooled  in  the  quenching  bath, 
and  any  which  might  cling  to  the  metal  is  easily  brushed  off,  or  it  can 
be  jarred  off  by  hitting  the  tool  a  sharp  rap.  This  is  also  considerable 
of  an  advantage  over  the  lead,  used  for  heating  steel,  as  frequently  spots 
of  lead  adhere  to  the  steel  and  are  difficult  to  remove. 

In  Fig.  103  is  shown  a  gas  or  oil  burning  furnace  that  was  designed 
especially  for  barium  chloride.  It  is  composed  of  a  sheet-metal  shell 
that  is  lined  with  a  special  fire-brick  to  withstand  the  high  temperatures 
that  are  required.  A  graphite  crucible  is  used  to  hold  the  chloride. 
After  the  crucible  is  set  in  the  furnace,  the  top,  which  fits  close  to  the 
crucible,  is  placed  on.  This  top  is  made  of  the  same  special  fire-brick 
that  forms  the  lining  of  the  furnace,  and  it  is  held  toegther  by  a  sheet- 
metal  band  with  two  lugs  and  a  clamping  nut.  This  band  is  provided 
with  two  handles  to  make  it  easily  movable  when  the  crucible  burns  out 


FURNACES  AND  FUELS  USED  FOR  HEAT-TREATMENT         179 

and  it  is  necessary  to  take  this  out  and  insert  a  new  one.  The  opening 
between  the  furnace  top  and  the  crucible  should  be  sealed  with  fire-clay 
to  prevent  the  gas  flames  from  attacking  the  barium  chloride  in  the  cru- 
cible, as  this  causes  unnecessary  fumes,  that  are  almost  unbearable,  to 
come  from  the  bath.  Two  per  cent,  of  soda  ash  (carbonate  of  soda)  is 
sometimes  added  to  prevent  these  fumes.  m 

The  gas  is  sent  into  the  furnace  at  an  angle,  as  this  gives  the  flame 
a  rotary  motion  that  will  create  an  even  heat  on  all  sides  of  the  crucible. 


FIG.  103.  —  Gas  or  oil  heated  barium  chloride  furnace. 

The  exhaust  opening  is  placed  at  the  side  of  the  gas  inlet,  and  as  close 
to  it  as  possible,  so  the  gas  will  make  the  complete  circuit  of  the  furnace 
chamber. 

In  Fig.  104  is  shown  a  line  drawing  of  the  same  furnace,  supplied  with 
an  enclosed  hood  permanently  fitted  to  it;  entrance  being  obtained  by 
means  of  a  large  door.  Through  this  hood  the  fumes  of  the  chloride 
are  carried  away  and  the  burned  gases  are  taken  from  the  furnace  through 
a  pipe  up  into  the  top  of  the  hood  and  thence  out  the  chimney. 


180 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


In  heating  steels  for  hardening  that  do  not  require  a  temperature 
of  over  1650°  F.,  a  mixture  of  chloride  of  barium  and  chloride  of  potas- 
sium, in  equal  parts,  gives  the  best  results.  As  the  required  temperature 
increases  the  chloride  of  potassium  should  be  reduced,  until  when  2000° 
F.  is  reached  it  should  be  left  out  altogether  and  only  the  pure  chloride 
of  barium  used.  In  all  cases  the  steel  should  be  heated  slowly  to  from 
600°  to  800°  F.  before  it  is  immersed  in  the  chloride  bath,  and  if  slowly 
heated  to  a  higher  temperature  it  will  do  no  harm. 

With  the  furnaces  shown  above,  steel  cannot  be  heated  to  over 
2100°  F.  without  its  becoming  pitted,  and  with  many  high-speed  steels 
it  is  desirous  to  heat  them  to  nearly  2500°.  This  is  doubtless  due  to  the 


Slag  Spout 


FIG.  104.  —  Barium  chloride  furnace  with  hood. 


fact  that  a  graphite  crucible  is  used  and  particles  of  it  separate  from 
the  crucible  and  float  in  the  chloride  bath  until  the  metal  is  inserted, 
when  they  attack  it  and  cause  pits  to  form.  With  an  electric  furnace, 
such  as  is  shown  in  Fig.  108,  this  is  entirely  overcome,  as  the  chloride 
holder  can  be  made  of  fire-brick  and  electrodes  inserted  in  the  bath. 
Owing  to  the  heat  being  generated  inside  of  the  bath,  instead  of  sur- 
rounding the  pot,  a  thin-walled  crucible  is  not  required,  hence  the 
chloride  pot  can  be  built  up  of  fire-brick  of  any  thickness  that  will  give 
it  the  needed  strength. 

In  starting  up  for  the  first  time  the  crucible  should  be  filled  with  the 
barium-chloride  that  can  be  bought  in  1000-pound  casks,  at  about  3  cents 


FURNACES    AND    FUELS    USED    FOR    HEAT-TREATMENT        181 

per  pound,  and  this  heated  slowly  until  it  melts  down.  After  this  more 
mixture  should  be  added  until  the  crucible  is  nearly  full.  After  the  bath 
is  melted,  tests  should  be  made  with  a  pyrometer  until  it  is  found  hot 
enough  for  hardening.  When  through  for  the  day  the  bath  should  be 
allowed  to  cool  with  the  furnace,  and  when  started  again  it  should  be 
heated  up  slowly. 

After  the  bath  is  thoroughly  liquid,  take  a  piece  of  steel  with  a  ground 
or  machined  surface,  heat  it  to  the  temperature  of  the  barium  chloride  and 
dip  it  in  the  cooling  bath,  then  brush  it  off,  and  if  there  are  no  " bubbles" 


FIG.  105.  —  Experimental  electric  furnace  for  heat-treating  steel. 

or  " blisters"  on  the  piece,  heat  the  bath  to  a  higher  temperature  and 
repeat  the  operation  until  they  do  appear,  and  then  note  the  temperature 
shown  by  the  pyrometer.  For  regular  use  a  temperature  about  50° 
below  the  point  at  which  bubbles  appear  is  the  best;  the  test  being  made 
with  a  new  clean  bath.  These  bubbles  are  the  indication  of  the  pitting 
that  occurs  at  temperatures  of  2100°  F.  or  over  when  the  gas  or  oil  fur- 
nace is  used  for  heating  the  barium  chloride.  As  the  bath  becomes  old 
or  dirty,  and  sluggish  from  steel  scale,  etc.,  bubbles  will  sometimes  appear 
at  a  lower  temperature  than  they  should,  in  which  case  the  remedy  is  a 
fresh  bath  in  the  crucible. 


182 


COMPOSITION    AND   HE  AT- TREATMENT    OF    STEEL 


ELECTRIC    FURNACES 


While  the  cost  of  electricity  for  heating  furnaces  is  probably  greater 
than  any  of  the  fuels,  the  results  obtained  by  its  use  in  heat-treating  steel 
are  better  than  by  any  other  method. 


FIG.  106.  —  Magnetic  furnace  for  hardening  steel. 

•  Electric  furnaces  may  be  placed  in  two  classes;  namely,  those  which 
use  electrodes  and  those  which  have  the  heating  chamber  wound  with 
platinum,  nickel,  or  ferro-nickel  wire,  this  being  covered  with  some 
product,  such  as  calcium  aluminate,  to  protect  it  from  the  action  of  the 
silicates'  of  the  lining.  Both  of  these  furnaces  are  lined  with  some  refrac- 
tory material,  but  the  latter  is  not  practical  for  large  furnaces,  and  is 


FURNACES    AND    FUELS    FOR    HEAT-TREATMENT 


183 


used  only  for  very  small  work  or  for  experimental  purposes.  This  style 
of  furnace  is  shown  in  Fig.  105. 

In  Figs.  106  and  107  is  shown  an  electric  furnace  in  which  a  magnet 
is  used  to  hold  the  work  until  it  reaches  the  point  of  recalescence,  where 
it  becomes  non-magnetic.  The  magnetic  attraction  is  then  broken  and 
the  work  can  drop  into  a  bath  for  quenching.  This  will  give  it  the  great- 
est hardness  it  is  possible  to  give  the  steel,  and  at  the  same  time  make 
the  grain  as  fine  and  the  molecules  as  cohesive  as  they  can  be  made  by 
heat  treatment. 

Electric  furnaces  similar  to  that  shown  in  Fig.  108  are  used  to  heat 
the  liquid  baths  described  above.  In  this  furnace  the  metallic  salt  baths 


FIG.  107.  —  Section  through  muffle  of 
magnetic  furnace. 

seem  to  be  the  most  appropriate.  These  salts  completely  prevent  con- 
tact between  the  white  hot  steel  and  the  air  during  the  heating,  as  well 
as  during  the  passage  to  the  quenching  bath;  the  steel  being  uniformly 
covered  with  a  protective  coat  of  the  salts  during  the  passage  of  the  steel 
from  the  furnace  to  the  quenching  bath.  On  immersion  in  the  cooling 
liquid  this  coating  immediately  leaves  it  and  the  surface  of  the  steel  always 
appears  smooth.  The  formation  of  scale  is  entirely  prevented  even  after 
tempering. 

The  source  of  heat  being  inside  the  bath  in  this  furnace  the  heat  is 
evenly  distributed  and  the  temperature  of  the  bath  is  uniform  throughout 
every  part  of  it.  High  temperatures  are  as  readily  obtained,  and  with 
as  little  watchfulness,  as  relatively  low  ones,  which  makes  it  easy  to 
determine  the  temperatures  desired  in  heat-treating  the  steel. 


184 


COMPOSITION   AND    HEAT-TREATMENT    OF    STEEL 


The  pyrometer  can  be  used  successfully  in  measuring  the  temperature 
of  the  bath.  The  temperature  of  the  bath  is  proportional  to  the  current, 
and  one  careful  determination  with  the  pyrometer  is  enough  to  afterward 
judge  the  temperature  of  the  bath  entirely  by  the  current. 


FIG.  108.  —  Sectional  views  of  electrode  furnace. 


This  style  of  furnace  requires  from  15  to  40  minutes  to  start,  accord- 
ing to  the  size.  The  cold  furnace  can  be  started  by  passing  the  current 
through  a  piece  of  carbon  until  this  becomes  white  hot  and  melts  the 
surrounding  salt,  which  then  becomes  conductive  and  in  turn  melts  the 
whole  mass.  When  finished  using  the  current  is  shut  off  and  the  salt 
bath  can  be  kept  molten  for  a  long  time  by  putting  a  cover  over  it. 


CHAPTER  IX 

ANNEALING  STEEL 
THEORY,  METHODS,  MATERIALS  USED  AND  APPLICATION 

IF  the  best  results  are  desired  from  steel,  after  it  has  been  rolled,  forged, 
pressed,  cast,  or  put  into  workable  shapes  in  any  other  way,  it  should 
be  annealed  before  any  other  work  is  done  upon  it.  This  removes  the 
internal  strains  that  are  set  up  in  the  metal,  when  working  it  into  the 
desired  shape  for  future  operation,  and  also  softens  the  steel.  It  can 
then  be  more  economically  machined  with  any  kind  of  cutting  tools, 
can  be  heat-treated  in  various  ways  without  the  danger  of  cracks  forming, 
and  will  have  greater  strength  and  endurance  when  put  to  its  intended 
use. 

The  annealing  of  steel  consists  in  carrying  it  above  the  temperature 
at  which  its  highest  point  of  transformation  occurs,  and  then  allowing  it 
to  cool  gradually.  This  point  of  transformation  is  that  at  which  the  steel 
becomes  non-magnetic  and  its  physical  structure  changes.  If  a  pyrom- 
eter is  used  to  indicate  the  temperature  of  the  steel  in  heating  or  cooling, 
it  will  show  a  point  at  which  the  rapid  change  in  temperature  ceases  for 
a  time,  and  the  recording  chart  will  show  a  line  nearly  at  right  angles  to 
that  of  the  rise  or  fall  curve.  At  this  point  all  the  molecules  have  become 
non-magnetic  and  a  new  crystal-size  of  grain  is  born.  This  refines  any 
large  or  coarse  crystals  that  may  have  been  produced  in  the  steel  by  for- 
mer methods  of  heating  or  working.  This  change  in  structure  releases 
any  strains  which  may  have  been  set  up  in  the  metal,  and  allows  them 
to  readjust  themselves  so  that  they  are  equalized  throughout  all  parts 
of  the  piece. 

This  temperature  of  the  point  of  transformation  varies  considerably 
in  different  steels.  This  is  partly  shown  by  Fig.  109,  which  was  plotted 
from  two  recording  pyrometer  charts.  Steels  vary  more  widely  than 
this,  however,  in  their  highest  recalescent  point;  it  being  affected  by  the 
various  ingredients  that  are  alloyed  with  the  metal. 

Another  operation,  sometimes  called  annealing,  is  that  of  partially 

185 


186 


COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 


destroying  the  effects  of  sudden  cooling  or  quenching.  In  this  the  anneal- 
ing temperature  is  kept  below  the  highest  point  of  transformation.  This 
operation  is  more  properly  named  tempering,  and  will  be  dealt  with  under 
that  title. 

As  a  general  rule  all  steel  should  be  annealed  after  every  process  in 
manufacturing  that  tends  to  throw  it  out  of  its  equilibrium,  such  as  forg- 
ing, rolling,  and  rough  machining,  in  order  to  return  it  to  its  natural 
state  of  repose. 

When  a  steel  ingot  has  been  poured  and  subjected  to  the  hammering 
process,  that  is  often  its  first  mechanical  working,  there  is  a  tendency  of 
the  crystals  to  crush.  This  will  bring  the  particles  of  the  metal  closer 
together,  but  there  is  a  limit  to  the  increase  in  the  density  which  can  be 


xauu 
1700 

/ 

IbUU 
1700 

1 

1600 
1500, 
1400 
1300 
1200 
11DO 
1000 
900 

800 
1 

/ 

1 

/ 

1500 
1400 
1300 
1200 
linn 

/ 

.. 

/ 

1 

jq 

1 

m 

/ 

1 

2 

H 

/ 

<o 

2 

to 

L 

$ 

/ 

p 

^ 

/ 

x 

x 

/ 

onn 

X' 

x 

snn 

X 

6       14.      12       10        8         6         4.        2         0       1C       14        12       10        8         64         20 

Time  In  Minutes                                                            Time  in  Minutes 

Time  In  Minutes  Time  in  Minutes 

FIG.  109.  —  Recalescent  point  curves,  plotted  from  two  pyrometer  charts. 

attained  in  this  manner  as  a  great  deformation  is  eventually  given  the  metal. 
This  metal  is  called  "  hammer-hard,"  and  some  metals  will  show  about 
twice  the  tensile  strength  after  being  hammered  to  the  limit  of  compres- 
sion that  they  will  when  in  the  normal  state. 

The  limit  of  compression  is  difficult  to  gage,  and  if  passed,  as  it  usually 
is  in  practice,  the  hammering  is  liable  to  cause  coarser  crystals  to  form 
where  it  has  squeezed  out  from  under  the  hammer  blows.  To  remove 
this  crystallization  and  refine  the  grain,  annealing  has  to  be  resorted  to, 
and  certain  laws  have  been  formulated  which  hold  good  on  annealing 
hammered  metal,  as  follows: 


ANNEALING  STEEL  187 

First.  —  Annealing  cannot  be  done  instantaneously,  but  its  effects 
are  the  greater  in  proportion  to  the  time  consumed.  A  rapid  change  takes 
place  at  the  start,  but  this  is  slower  and  slower  as  the  time  progresses, 
and  there  is  a  tendency  toward  a  fixed  limit  for  the  decrease  in  hammer- 
hardness  at  each  degree  of  temperature. 

Second.  —  The  higher  the  annealing  temperature,  the  lower  will  be 
the  limit  toward  which  hammer-hardness  tends;  in  practice  the  more 
rapidly  will  this  limit  be  attained. 

Third.  —  The  annealing  effects  are  practically  completed  when  a 
certain  temperature  has  been  reached,  and  any  increase  above  that  does 
not  further  reduce  the  tensile  strength  as  this  has  reached  the  lowest 
point  possible  for  the  steel  operated  on. 

The  effect  called  " crystallization  of  annealing"  may  start  at  this  tem- 
perature and  become  more  pronounced  as  -the  annealing  process  con- 
.tinues.  It  causes  the  reduction  of  area  to  decrease,  and  if  very  pronounced 
this  may  become  nil,  together  with  the  elongation,  while  the  tensile  strength 
is  much  reduced.  Another  phenomenon  might  be  mentioned  here,  and 
that  is  spontaneous  annealing.  Thus,  if  hardened  steel  be  left  to  itself  it 
will  anneal  of  itself,  the  only  factor  entering  into  this  phenomenon  being 
time.  As  this  time,  however,  covers  such  a  long  period  and  the  annealing 
process  is  such  a  slow  one  the  principle  is  of  no  importance  from  a  prac- 
tical standpoint. 

From  the  above  may  be  deduced  three  practical  rules  to  adopt  in 
annealing  steel,  these  being: 

First.  —  A  quenched  or  hammered  piece  must  be  heated  to  a  tem- 
perature above  its  highest  point  of  transformation,  but  as  close  to  this 
point  as  possible. 

Second.  —  This  temperature  must  be  retained  long  enough  to  allow 
the  entire  piece  to  reach  an  even  temperature,  but  it  must  not  be  pro- 
longed beyond  it. 

Third.  —  The  rate  of  cooling  must  be  sufficiently  slow  to  prevent 
any  hardening  taking  place,  not  even  superficial  hardening. 

In  applying  these  rules  we  find  that  extra  low-carbon  steel  should 
be  annealed  at  1650°  F.,  and  extra  high-carbon  steel  at  1375°.  The 
time  of  annealing  varies  with  the  size  and  shape  of  the  piece  as  well  as 
with  the  work  which  it  has  to  perform.  The  more  important  this  work 
is,  the  more  prolonged  should  be  the  annealing  process.  Intricate  pieces 
with  thin  and  thick  sections  have  to  be  handled  with  extra  care,  and  some- 
times materials  are  brought  into  use  to  retard  the  cooling  of  the  thin 
section,  as  ordinarily  a  thin  section  will  cool  quickly  in  comparison  with 
the  thick  one,  and  consequently  be  that  much  harder. 

To  insure  slow  cooling,  when  a  slow-cooling  furnace  is  not  obtainable, 
the  work  should  be  packed  in  some  non-carbonizing  material,  in  an  iron 


188 


COMPOSITION  AND   HEAT-TREATMENT   OF  STEEL 


box  lined  with  fire-brick  similar  to  the  one  shown  in  Fig.  110.  The  whole 
can  then  be  heated  in  a  furnace  and  set  out  on  the  floor  to  cool  as  the 
thickness  of  the  materials  prevents  rapid  cooling.  This  will  also  tend 
to  prevent  the  pieces  from  scaling  as  they  do  not  come  in  contact  with 
the  oxidizing  influences  of  the  atmosphere.  When  the  temperature  of 
the  pieces  has  dropped  to  550°  F.  they  may  be  removed  from  the  box 
as  the  annealing  process  has  ceased,  and  there  will  be  no  danger  of  their 
air-hardening. 

As  it  is  generally  agreed  upon  that  steel  should  not  be  heated  much 
above  the  point  of  transformation  in  the  annealing  process  it  would  be 
well  to  give  the  reasons.  The  nine  laws  formulated  by  Prof.  H.  M.  Howe, 
after  many  tests  by  himself  and  others,  cover  the  ground  so  thoroughly 
that  they  are  here  given. 

First  Law.  —  When  a  given  steel  is  heated  to  a  temperature  above 
the  highest  point  of  transformation  the  grain  assumes  a  definite  size, 
characteristic  of  the  temperature.  We  call  this  the  normal  size. 


FIG.  110.  —  Cast-iron  box  for  annealing. 

Second  Law.  —  The  size  of  the  grain  increases  in  proportion  to  the 
temperature,  counted  from  the  highest  point  of  transformation. 

Third  Law.  —  The  influence  of  the  temperature  is  the  more  pronounced 
the  greater  the  carbon  content  of  the  steel.  In  other  words,  for  the  same 
annealing  temperature  the  normal  grain  of  the  steel  is  coarser  the  greater 
the  carbon  content. 

Fourth  Law.  —  If  a  steel  is  raised  to  a  temperature  above  its  highest 
point  of  transformation,  and  if  in  consequence  of  previous  treatment 
the  steel  possesses  a  finer  grain  than  the  normal,  the  grain  of  the  metal 
becomes  coarser  until  it  is  equal  to  the  normal  grain. 

Fifth  Law.  —  In  order  to  attain  the  normal  grain  for  any  temperature, 
the  metal  must  be  maintained  at  this  temperature  for  some  time. 

Sixth  Law.  —  If  the  metal  is  heated  to  a  certain  temperature  and  has 
assumed  the  normal  grain  for  this  temperature,  and  if  it  is  then  main- 
tained at  a  somewhat  lower  temperature,  but  still  above  the  point  of 


ANNEALING  STEEL  189 

transformation,  the  size  of  the  grain  is  not  reduced,  provided  the  metal 
is  not  reduced  below  the  point  of  transformation. 

To  illustrate  this,  if  a  steel  is  carried  to  2200°  F. ;  the  grain  then  becomes 
of  the  size  characteristic  of  this  temperature;  if  the  temperature  is  then 
lowered  to  1650°  there  will  be  no  change  in  the  size  of  the  grain.  It  would 
be  quite  different,  however,  if  instead  of  cooling  the  metal  directly  to 
1650°,  it  had  been  cooled  down  to  925°,  which  is  much  below  the  point 
of  transformation,  and  then  reheated  to  1650°. 

Seventh  Law.  —  If  the  temperature  of  a  steel  remains  below  the  point 
of  transformation  its  grain  does  not  change. 

Eighth  Law.  —  If  a  steel  is  cooled  slowly  after  having  been  heated  to 
above  its  point  of  transformation,  it  possesses  substantially  the  same 
grain  as  that  which  it  possessed  at  the  maximum  temperature. 

Ninth  Law.  —  From  this  it  may  be  deduced  that  the  grain  of  a  metal, 
after  annealing,  is  the  coarser  the  higher  the  temperature  to  which  it 
has  been  raised  above  the  point  of  transformation. 

While  the  relation  existing  between  the  annealing  temperature  and 
the  mechanical  properties  has  not  been  fully  determined,  enough  is  known 
to  establish  certain  rules  that  are  beneficial  in  a  practical  way.  A 
coarse-grained  metal  is  more  brittle  than  a  fine-grained,  and  therefore 
any  change  in  the  size  of  the  grain  will  affect  the  strength  of  the  steel. 
As  the  annealing  temperature  affects  the  size  of  the  grain,  a  steel  that 
is  heated  to  a  variable  temperature  and  slowly  cooled  will  alter  its  mechan- 
ical properties  about  as  follows: 

First.  —  The  tensile  strength  slightly  increases  with  the  increase  in 
temperature  up  to  2375°  F.,  after  which  it  rapidly  decreases. 

Second.  —  The  elastic  limit  passes  through  a  minimum  at  the  highest 
point  of  transformation,  but  increases  slightly  when  the  temperature 
passes  this  point,  and  then  decreases  as  this  point  is  exceeded  by  175°  F. 
The  slower  it  is  cooled  from  the  point  to  which  it  has  been  heated  the 
lower  will  be  the  elastic  limit. 

Third.  —  The  elongation  decreases  as  the  annealing  temperature 
increases,  and  this  decrease  is  very  important  when  the  temperature 
attains  2375°  F.  This  makes  it  necessary  to  keep  the  annealing  tem- 
perature a  little  above,  but  as  close  to  the  point  of  transformation  as 
possible. 

With  these  points  taken  into  consideration  it  will  be  seen  that  the 
annealing  of  steels  cannot  be  too  carefully  done  if  the  best  results  are 
to  be  obtained,  and  especially  is  this  so  of  the  high-grade  alloy  steels 
which  are  being  used  more  and  more  every  day.  It  has  been  shown  that 
if  the  heat  treatment  is  carried  out  in  a  manner  that  will  produce  sor- 
bite,  the  tensile  strength  is  much  higher  and  the  elongation  is  slightly 
greater  than  when  the  metal  is  simply  annealed.  To  obtain  sorbite  it 


190  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

is  necessary  to  quench  above  the  point  of  transformation  and  then  reheat 
to  from  575°  to  1300°  F.,  according  to  the  composition  of  the  metal  and 
the  hardness  desired,  then  cool  in  air  or  in  water. 

APPARATUS   FOR  ANNEALING 

The  furnaces  used  for  annealing  are  the  same  as  those  used  for  other 
heat-treating  operations,  unless  enough  pieces  are  annealed  to  install  a 
slow-cooling  furnace,  and  then  it  is  only  the  accessories  that  are  different. 
The  materials  in  which  to  pack  the  metal  are  nearly  as  numerous  as  the 
baths  for  quenching,  and  where  a  few  years  ago  the  ashes  from  the  forge 
were  all  that  were  considered  necessary  for  properly  annealing  a  piece 
of  steel,  to-day  many  special  preparations  are  being  manufactured  and 
sold  for  this  purpose. 

The  more  common  materials  used  for  annealing  are  powdered  char- 
coal, charred  bone,  charred  leather,  mica,  slacked  lime,  sawdust,  sand, 
fire-clay,  magnesia,  and  refractory  earth.  The  piece  to  be  annealed  is  usu- 
ally packed  in  a  cast-iron  box,  similar  to  Fig.  110;  using  some  of  these 
materials  or  combinations  of  them  for  the  packing,  the  whole  is  then  heated 
in  a  furnace  to  the  proper  temperature  and  set  aside,  with  the  cover  left 
on,  to  cool  gradually  to  the  atmospheric  temperature. 

For  certain  kinds  of  steel  these  materials  give  good  results;  but  for 
all  kinds  of  steels  and  for  all  grades  of  annealing,  the  slow-cooling  furnace 
no  doubt  gives  the  best  satisfaction,  as  the  temperature  can  be  easily 
raised  to  the  right  point,  kept  there  as  long  as  necessary,  and  then  regu- 
lated to  cool  down  automatically  and  as  slowly  as  is  desired.  The  gas, 
oil,  and  electric  furnaces  are  the  easiest  to  handle  and  regulate. 

As  an  example  of  this  a  maker  of  high-grade  files  uses  a  gas  furnace 
in  which  to  anneal  the  files,  and  they  are  packed  in  this  with  the  tangs 
outward.  The  furnace  is  heated  up  and  kept  at  a  temperature  of  1500°  F. 
for  4  hours,  and  then  allowed  to  slowly  cool  during  two  nights  and  one 
day.  The  flame  is  from  a  vaporized  naphtha  preparation  that  is  free  from 
injurious  elements,  such  as  sulphur,  and  is  supplied  with  a  slight  under- 
supply  of  oxygen,  so  there  will  be  no  danger  of  its  oxidizing  the  metal. 
The  files  are  submitted  to  the  direct  action  of  this  flame,  which  fills  every 
part  of  the  heating  chamber,  so  that  the  end  and  sides,  as  well  as  the  cen- 
ter, can  be  maintained  at  the  same  even  temperature.  By  having  a 
constant  pressure  and  volume  for  the  air  and  gas  the  flame  is  easily  con- 
trolled and  is  non-oxidizing,  therefore  there  is  no  pitting  or  blistering  of 
the  files.  They  do,  however,  have  a  very  thin  scale,  that  is  caused  by 
the  air  that  leaks  into  the  furnace  while  it  is  cooling,  but  this  is  not  enough 
to  do  any  practical  damage. 

There  is  one  notable  exception  to  these  annealing  rules,  and  that  is 
in  the  case  of  Hatfield's  manganese  steel,  which  is  so  brittle  when  cast 


ANNEALING  STEEL  191 

as  to  be  useless.  It  is  toughened,  or  tempered,  by  heating  and  quench- 
ing, and  is  hardened  by  slow  cooling. 

While  high-speed  steel  has  heretofore  been  annealed  in  practically 
the  same  way  as  the  carbon  steels,  and  therefore  subject  to  the  above 
rules,  it  is  hardened  by  rules  altogether  different  from  those  governing 
the  carbon  .steels. 

A  new  method  of  annealing  high-speed  steel  that  is  a  great  improve- 
ment over  this  old  one  has  been  discovered  and  perfected  by  C.  U.  Scott 
of  Davenport,  Iowa,  at  the  Rock  Island  arsenal.  He  places  the  high- 
speed steel  in  a  furnace  that  is  heated  to  not  over  750  °F.,  and  raises  the 
temperature  slowly  to  1300°  F.  He  then  shuts  off  the  heat  and  allows 
both  the  steel  and  the  furnace  to  cool  to  not  over  750°  F.,  or  to  atmos- 
pheric temperature  if  desired.  The  steel  is  then  reheated  to  a  temper- 
ature of  1300°  F.,  and  held  there  for  30  minutes  and  then  cooled  in  the 
air. 

In  this  way  any  high-speed  steel  that  is  not  over  1  inch  square  can 
be  annealed  in  40  minutes,  and  it  does  not  take  over  one  hour  for  large 
stock.  The  metal  is  made  as  soft  and  it  machines  as  readily  as  steel 
annealed  by  any  other  method.  Whether  the  steel  is  entirely  cooled 
after  the  first  heating  or  whether  the  temperature  varies  a  few  degrees 
from  the  1300  is  immaterial. 

Another  hardener  on  trying  out  this  method  got  his  data  mixed  and 
obtained  the  same  degree  of  softness  in  another  way.  He  heated  the 
steel  to  a  low  red,  and  held  the  temperature  at  that  point  for  30  minutes. 
He  then  let  it  cool  down  and  afterward  reheated  it  and  immediately 
let  it  cool  down  until  it  was  at  the  correct  temperature  for  water  annealing 
and  then  laid  it  in  the  ashes  until  it  was  cold  enough  to  handle. 


CHAPTER  X 
HARDENING  STEEL 

ALTERATIONS  IN  STRUCTURE,  INFLUENCE  OF  COMPOSITION,  AND  RESULTS 

OBTAINED 

HARDENING,  when  applied  to  steel,  is  generally  understood  to  mean 
the  heating  of  the  metal  to  a  high  temperature  and  then  plunging  it  into 
a  bath  for  the  purpose  of  suddenly  cooling  it.  While  this  definition  holds 
good  on  most  steels,  a  few  alloying  materials  now  used  reverse  this  and 
make  the  metals  air-hardening,  that  is,  their  hardest  and  toughest  state 
is  obtained  by  a  slow-cooling  process  rather  than  a  sudden  one. 

Two  reasons  might  be  assigned  for  the  desirability  of  hardening  steel, 
and  these  are:  First,  to  give  the  steel  a  cutting  edge  such  as  is  required 
for  all  cutting  tools,  and,  second,  to  alter  the  static  strength  and  dynamic 
qualities  of  the  metal  so  it  will  give  the  best  results  for  the  moving  parts 
of  machinery. 

In  this  second  case  steels  may  be  altered  by  quenching  from  a  high 
temperature  and  tempering,  to  an  extent  that  will  greatly  improve  their 
wearing  qualities,  tensile  strength,  elastic  limit,  magnetic  qualities,  or 
resistance  to  shock,  and  yet  not  be  capable  of  attaining  a  hardness  that 
will  not  allow  a  file  to  cut  it;  this  being  the  usual  test  of  hardness  applied 
in  the  shop.  Thus,  generally  speaking,  all  steels  may  be  hardened, 
although  some  may  have  a  low  carbon  content. 

To  harden  steel,  therefore,  it  is  necessary  for  the  heating  to  produce 
a  change  in  the  structure,  and  the  quenching,  which  follows  the  heating, 
retains  a  whole  or  a  part  of  the  changes  produced  by  this  change  of  struc- 
ture. It  is  therefore  necessary,  as  in  annealing,  that  the  temperature  of 
the  steel  be  raised  to  a  point  slightly  above  the  point  of  transformation 
or  recalescent  point. 

As  the  point  of  transformation  varies  with  different  ingredients  which 
are  alloyed  with  steel,  it  is  necessary  to  find  out  where  it  is  in  the 
steel  to  be  hardened.  A  steel  may  be  heated  to  1300°  F.  —  which  is 
above  the  point  of  transformation  in  some  steels  —  and  no  change  in 
structure  will  take  place,  and  therefore  no  results  in  hardness  will  be 
obtained.  If  the  same  piece  is  heated  to  1650°  —  which  we  will  consider 
the  point  of  transformation  in  this  piece  —  the  intermolecular  transforma- 

192 


UNIVERSITY 

Of 


HARDENING  STEEL  193 


tion,  which  consists  of  the  passage  of  the  carbon  from  the  combined  into 
the  dissolved  state,  will  take  place  and  the  steel  will  assume  the  hardest 
state  it  is  capable  of,  if  properly  cooled. 

Thus  the  factors  that  have  an  influence  on  the  results  of  hardening 
are:  First,  the  nature  and  composition  of  the  metal;  second,  the  tem- 
perature of  the  metal  when  quenched,  and,  third,  the  nature,  volume, 
and  temperature  of  the  quenching  bath. 

MICROSCOPICAL   EXAMINATION 

The  nature  of  these  different  factors  is  shown  to  a  large  extent  by 
quenching  the  metal  at  different  temperatures,  polishing  the  surface, 
attacking  it  with  picric  acid,  tincture  of  iodine,  hydrofluoric  acid,  or 
any  other  etching  materials  and  examining  it  under  a  microscope. 

FEARITE.  —  Steel  containing  less  than  0.85%  carbon  will  show  small 
dark  masses,  if  etched  with  picric  acid,  which  are  the  more  numerous 
the  closer  the  carbon  content  is  to  0.85%.  At  this  percentage  they  cover 
the  entire  surface.  These  masses  show  alternate  layers  which  are  fer- 
rite  —  pure  iron  —  and  an  iron  carbide  called  cementite.  The  ferrite 
being  the  softest  constituent  of  steel,  it  will  indent  when  polished  and 
the  cementite  will  stand  out  in  relief. 

Ferrite  is  the  carrier  for  all  of  the  alloying  elements  in  the  high-grade 
steels.  It  is  the  principal  constituent  of  all  steels  and  the  predominating 
one  in  low-carbon  steels.  It  has  one  peculiarity  which  is  very  important, 
and  that  is,  that  when  heated  to  about  1400°  F.  it  undergoes  a  sudden 
change  which  is  shown  by  its  absorption  of  heat.  It  then  loses  its  power 
to  attract  a  magnet  as  well  as  changing  its  specific  heat  and  several  other 
properties.  No  alteration,  however,  takes  place  in  its  chemical  com- 
position. 

At  1550°  F.  it  again  shows  changes  by  absorbing  heat  and  its  prop- 
erties are  again  changed.  (See  chart  1,  page  67.)  Its  electrical  conduc- 
tivity has  changed  and  also  its  crystalline  form.  These  changes  occur  both 
in  the  rise  and  fall  of  the  temperature,  and  have  been  called  by  different 
metallurgists  the  points  of  transformation,  the  recalescence  points,  and 
the  critical  temperatures;  all  of  which  mean  the  same. 

Ferrite  is  shown  in  Figs.  Ill,  112,  113,  114,  and  117. 

CEMENTITE  is  the  carbide  of  iron,  and  is  expressed  by  the  following 
formula:  Fe3C,  which  means  ferrite  —  which  is  pure  iron  —  3  atoms 
for  every  one  atom  of  carbon.  It  is  the  second  constituent  in  importance 
in  steel  —  ferrite  being  first  —  and  is  very  hard  and  brittle.  Practically 
all  of  the  carbon  is  present  in  this  form,  and  it  usually  crystallizes  in 
thin  flat  plates.  Cementite  does  not  exist  in  pure  iron,  which  contains 
no  carbon,  and  of  itself  contains  about  6.6%  of  carbon,  which  is  about 


194 


COMPOSITION    AND   HEAT-TREATMENT    OF   STEEL 


one-fifteenth  of  it.     Two  extremes  of  cementite  formation  are  shown 
in  Figs.  Ill  and  112. 

PEARLITE.  —  Pearlite  is  an  intimate  mixture  of  ferrite  and  cementite 


FIG.  111.  —  Ferrite  with  very  thin  con- 
tinuous cementite  skeleton.  Low  car- 
bon. Magnified  250  diameters. 


FIG.  112. — Ferrite,  white.  Cementite, 
black.  Magnified  250  diameters. 


in  the  definite  proportions  of  32  parts  ferrite  to  5  of  cementite,  equivalent 
to  .85%  carbon.     It  has  the  appearance  of  mother  of  pearl,  from  which 


FIG.  113.  —  Ferrite  matrix  with  sepa- 
rated pearlite  islands.  Magnified 
250  diameters. 


FIG.  1 14.  —  Ferrite,  white.     Pearlite, 
black.   Magnified  250  diameters. 


it  derives  its  name.     It  exists  in  a  lamellar  formation,  which  is  alternate 
plates  of  ferrite  and  cementite,  or  in  a  granular  formation,  which  is  inter- 


HARDENING    STEEL  195 

mingling  grains  of  ferrite  and  cementite.  A  normal  steel,  containing 
0.85%  carbon,  consists  of  100%  pearlite;  below  this  carbon  content  it 
contains  pearlite  and  excess  ferrite;  while  if  the  total  carbon  exceeds 
0.85%  the  constituent  excess  would  be  cementite  instead  of  ferrite.  Pearl- 
ite is  shown  in  Figs.  113  and  114. 

MARTENSITE  AND  HARDEN ITE.  —  Leaving  the  steels  that  have  been 
cooled  slowly,  and  taking  up  those  which  have  been  quenched  from  a 
given  temperature,  and  hardened,  we  find  that  a  steel  containing  about 
0.85%  carbon,  if  heated  to  about  1400°  F.  and  quenched,  will  show  under 
the  microscope  extremely  fine  lines  intersecting  each  other  in  the  direc- 
tion of  the  sides  of  an  equilateral  triangle.  This  constituent  has  been 
named  martensite  in  honor  of  Professor  Martens.  It  is  the  principal 
constituent  of  all  ordinary  hardened  steels  that  have  a  carbon  content 
above  0.16%,  and  tempered  steels  owe  their  quality  of  hardness  to  it. 
It  is  so  hard  that  a  needle  will  not  scratch  it  after  the  metal  has  been 
polished. 

In  steels  containing  over  0.85%  carbon  the  martensite  is  said  to  be 
saturated  and  shows  slightly  different  under  the  microscope.  This  has 
been  called  hardenite  by  some,  which  word  is  often  used  in  French  and 
German  books. 

Martensite  is  shown  in  Figs.  115  and  116. 

SORBITE  is  a  constituent  between  martensite  and  pearlite,  and  chiefly 
differs  from  pearlite  by  the  constituents  not  quite  perfectly  developing. 
This  is  drawing  the  line  pretty  fine,  but  the  sorbitic  structure  is  finer  than 
the  pearlitic,  and  it  is  considered  the  extreme  opposite  of  the  crystalline 
structure.  The  sorbitic  structure  is  considered  necessary  in  metals  that 
have  to  resist  wear  and  erosion,  and  the  natural  formation  of  this  struc- 
ture is  rendered  possible  by  the  addition  of  certain  alloying  elements. 
In  hardened  steel,  sorbite  is  considered  as  the  transition  from  martensite 
to  pearlite. 

The  sorbitic  structure  may  be  obtained  when  the  cooling  is  not  as 
rapid  as  that  of  quenching,  but  still  much  faster  than  the  slow  cooling 
for  annealing;  by  quenching  immediately  below,  or  just  at  the  end  of 
cooling  through  the  critical  range;  by  cooling  pretty  fast  through  the 
critical  range  without  actual  quenching;  or  by  rapidly  cooling  the  steel 
and  then  reheating  to  about  1100°  F.  Sorbite  is  not  clearly  defined  in 
micro-photographs,  but  Fig.  117  shows  it  fairly  well,  with  ferrite. 

AUSTENITE. — High-carbon  steels  that  contain  over  1.10%  of  carbon 
and  are  suddenly  cooled  from  a  temperature  of  2000°  F.  will  show  a  con- 
stituent, in  addition  to  martensite,  which  may  be  distinguished  from  it 
by  a  different  color.  If  etched  with  nitrate  of  ammonia,  or  with  a  10% 
solution  of  hydrochloric  acid,  it  will  show  white.  This  constituent  is 


196 


COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 


softer  than  martensite,  and  is  easily  scratched  with  a  needle.  It  is  essen- 
tially a  solid  solution  of  carbon  in  gamma  iron.  It  has  been  named  aus- 
tenite  after  Prof.  Robert  Austen. 


FIG.  115.  —  Martensite  formation. 
Magnified  250  diameters. 


F.G.  116.—  Martensite.     Magnified  200 
diameters. 


Austenite  is  difficult  to  preserve  throughout  the  whole  structure  of 
the  steel.  Quenching  in  a  bath  that  has  a  temperature  below  the  freezing 
point,  or  any  other  means  which  will  cool  it  rapidly,  will  aid  in  preserving 


FIG.  117.  —  Ferrite  and  sorbite. 
Magnified  250  diameters. 


FIG.  118.  —  Austenite,  white.     Troostite, 
black.     Magnified  50  diameters. 


it.  Tempering  the  metal  afterward,  however,  loses  the  austenite,  and 
it  is  not  of  much  practical  use  owing  to  the  high  temperature  at  which 
it  is  obtained.  Fig.  118  shows  the  austenite  formation. 


HARDENING    STEEL  197 

TROOSTITE.  —  If  the  steel  is  quenched  during  or  just  above  its  trans- 
formation in  a  bath  of  little  activity,  such  as  oil,  or  if  it  is  hardened  in 
the  usual  way,  and  then  tempered,  we  obtain  a  constituent  which  will 
show  jet  black  if  polished  and  etched  with  picric  acid,  or  if  etched  with 
a  tincture  of  iodine  it  will  show  white.  This  has  been  named  troostite  in 
honor  of  Prof.  M.  Troost. 

Troostite  is  also  softer  than  martensite,  as  it  can  be  scratched  with 
a  needle.  It  is  a  transition  product  between  martensite  and  sorbite,  and 
is  found  plentifully  in  tempered  steels  as  it  is  a  product  of  the  usual  tem- 
pering operations.  It  shades  gradually  into  the  sorbite,  but  is  very  sharp 
in  its  divisions  from  martensite.  Troostite  is  shown  black  in  Fig.  118  and 
white  in  Fig.  119. 


FIG.  119.  —  Martensite,  black.     Troostite, 
white.     Magnified  350  diameters. 

In  subjecting  steel  to  different  heat  treatments  we  can  change  the 
constituents  from  pearlite  to  martensite  or  hardenite,  sorbite,  austenite, 
and  troostite,  and  back  again  through  these  different  stages,  and  by  exam- 
ining them  with  the  microscope  we  can  judge  very  closely  the  treatment 
they  have  been  subjected  to. 

By  making  these  changes  we  also  change  its  constitution,  its  static 
strengths,  and  its  dynamic  properties.  This  is  where  the  practical  appli- 
cation of  this  knowledge  aids  the  engineer  or  designer  in  designing  the 
moving  as  well  as  other  parts  of  machinery  so  as  to  get  the  best  results 
from  the  smallest  quantity  of  material. 

EFFECT    OF    COMPOSITION   AND    HARDENING 

The  constitution  of  a  given  steel  is  not  the  same  in  the  hardened  as 
in  the  normal  state,  owing  to  the  carbon  not  being  in  the  same  state. 
In  the  annealed  or  normal  steel  it  is  as  cementite,  while  in  a  hardened 


198 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


steel  it  is  in  a  state  of  solution,  which  we  may  call  martensite;  and  this 
contains  more  or  less  carbon  according  to  the  original  carbon  content 
of  the  steel.  The  composition,  and  therefore  the  mechanical  properties, 
depend  principally  upon  the  carbon  content,  the  mechanical  properties 
being  changed  slowly  and  gradually  by  an  increase  in  carbon. 

TABLE    1.     COMPOSITION 


Carboniz- 
ing Steel 

Very  Low 
Carbon 

Low 
Carbon 

Medium 
Carbon 

High 
Carbon 

Very  High 
Carbon 

Carbon  

0.10 

0.14 

0.23 

0.52 

0.60 

0.72 

Silicon                      

0.09 

0.05 

0.15 

0.18 

0.10 

0.17 

Manganese 

0.19 

0.33 

0.45 

0.35 

040 

038 

Phosphorus  

0.016 

0.023 

0.091 

0.021 

0.035 

0.03 

Sulphur  

0.025 

0.052 

0.062 

0.043 

0.025 

0.06 

MECHANICAL     PROPERTIES     WHEN     ANNEALED 


Tensile  Strength  (in  pounds 
per  square  inch) 

60,300 

61,500 

66,500 

97,800 

116,400 

130,700 

Elastic  Limit  (in  pounds  per 
square  inch)  
Elongation  (percentage  in  2 
inches)    

36,300 
29 

35,200 
27 

41,200 
26 

52,600 
20 

66,500 
14 

75,800 
9 

MECHANICAL     PROPERTIES     WHEN     HARDENED 


Tensile  Strength  (in  pounds 

per  square  inch)  

66,400 

73,100 

99,400 

132,100 

153,400 

180,100 

Elastic  Limit  (in  pounds  per 

square  inch)  

40,300 

39,600 

54,000 

81,400 

102,100 

105,500 

Elongation  (percentage  in  2 

inches) 

24 

22 

14 

9 

4 

0 

EFFECT   OF    COMPOSITION    AND    HARDENING    ON    THE    STRENGTH  OF   CARBON 

STEEL 

This  is  best  shown  by  the  above  table  ,  in  which  it  will  be  seen  that 
the  tensile  strength  and  elastic  limit  gradually  increased  with  the  increase 
in  the  percentage  of  carbon,  both  in  the  annealed  and  hardened  state, 
while  the  elongation  gradually  decreased.  These  tests  were  made  with  a 
bar  |  inch  in  diameter  and  4  inches  in  length.  It  will  also  be  seen  that 
there  was  considerable  change  in  the  steels  that  were  too  low  in  carbon  to 
be  made  so  hard  that' they  could  not  be  filed.  The  reduction  in  elonga- 
tion when  the  test  bars  were  heated  and  quenched  showed  that  the  metal 
was  harder  than  when  in  the  annealed  state. 

A  hardening  process  that  will  produce  a  steel  that  is  as  homogeneous 


HARDENING   STEEL  199 

as  possible  is  always  sought  for  in  practice.  This  is  easily  obtained  in 
a  high-carbon  steel,  and  especially  if  it  contains  0.85%  carbon,  by  passing 
the  upper  recalescent  point  before  quenching.  The  desired  homogeneity 
is  not  so  easily  obtained,  however,  in  the  low-carbon  steels  as  they  have 
several  points  of  transformation.  If  these  are  quenched  at  a  point  a  little 
above  the  lowest  point  of  transformation,  the  carbon  will  be  in  solution, 
but  the  solution  is  not  homogeneous.  To  obtain  this  result  it  is  neces- 
sary that  the  quenching  be  done  from  a  little  above  the  highest  point  of 
transformation.  This  is  higher  in  low-  than  in  high-carbon  steels.  In 
practice  this  calls  for  a  quenching  of  the  low-carbon  steels  at  about 
1650°  F.,  while  a  high-carbon  steel  should  be  quenched  at  about  1450°. 

The  degree  of  temperature,  above  the  critical  point,  to  which  steel 
can  be  heated  in  practical  commercial  work  and  still  give  good  results 
is  also  quite  important.  If  a  piece  of  steel  be  quenched  from  different 
temperatures  above  the  point  of  transformation  and  examined  under  a 
microscope  we  find  that  the  higher  we  go  the  coarser  will  be  the  marten- 
site,  and  the  lines  will  be  more  visible.  If  we  raise  this  temperature  a 
few  hundred  degrees  above  the  critical  point  and  quench  in  a  very  cold 
bath,  austenite  makes  its  appearance.  In  regard  to  the  mechanical 
properties  the  higher  the  temperature  above  the  critical  point  the  lower 
will  be  the  tensile  strength  and  the  less  will  be  the  hardness  of  the  steel. 
The  elongation  will  also  show  a  decrease  and  this  will  mean  that  the  steel 
becomes  more  brittle  with  each  increase  in  the  temperature. 

This  coarsening  of  the  martensite,  the  reduction  of  both  the  tensile 
strength  and  elongation  and  the  crystallization  spoken  of  some  few  para- 
graphs back,  have  led  to  the  conclusion  that,  in  practice,  40°  F.  above 
the  highest  point  of  transformation  is  the  extreme  limit  that  steel  should 
be  raised  to  obtain  the  best  results  in  hardening.  The  same  figure  also 
holds  good  for  annealing. 

The  following  results  are  obtained  in  hardening  steel:  All  steels  may 
be  hardened,  but  if  the  carbon  content  is  over  0.30%  the  effect  is  more 
pronounced.  Hardening  increases  the  tensile  strength  and  elastic  limit 
and  reduces  the  elongation,  the  effect  being  greater  the  greater  the  carbon 
content.  Quenching  at  the  proper  temperature  gives  the  metal  a  greater 
homogeneity  and  this  aids  the  resistance  to  shock,  especially  in  low- 
carbon  steels;  steel  should  not  have  the  hardening  temperature  raised 
more  than  40  degrees  above  the  highest  point  of  transformation,  as 
beyond  that  it  no  longer  has  the  same  qualities. 

BATHS   FOR   HARDENING 

As  it  is  necessary  to  maintain  the  metal  in  the  state  it  was  at  the 
moment  quenching  begins,  the  quenching  bath  is  a  very  important  part 
of  the  process  of  hardening.  The  rate  of  cooling  is  never  swift  enough 


200  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

to  secure  perfection,  and  the  intermolecular  transformation  will  be  more 
or  less  complete  according  to  the  rate  of  cooling.  The  better  the  bath 
the  nearer  to  perfection  we  will  be  able  to  arrive. 

The  baths  for  quenching  are  composed  of  a  large  variety  of  materials. 
Some  of  the  more  commonly  used  are  as  follows;  they  being  arranged 
according  to  their  intensity  on  0.85%  carbon  steel:  Mercury;  water  with 
sulphuric  acid  added;  nitrate  of  potassium;  sal  ammoniac;  common  salt; 
carbonate  of  lime;  carbonate  of  magnesia;  pure  water;  water  containing 
soap,  sugar,  dextrine,  or  alcohol;  sweet  milk;  various  oils;  beef  suet; 
tallow;  wax.  These  baths,  however,  do  not  act  under  all  conditions 
with  the  same  relative  intensity,  as  their  conductivity  and  viscosity  vary 
greatly  with  the  temperature,  and  their  curves  of  intensity  are  therefore 
very  irregular  and  cross  each  other  frequently.  Notwithstanding  the 
many  special  compounds  that  have  been  exploited  for  hardening,  there 
are  no  virtues,  or  hardening  and  toughening  properties,  in  any  quenching 
bath  beyond  the  degree  of  rapidity  with  which  it  conducts  the  heat  out 
of  the  piece  being  quenched. 

With  the  exception  of  the  oils  and  some  of  the  greases,  the  quenching 
effect  increases  as  the  temperature  of  the  bath  lowers.  Thus  water  at 
60°  will  make  steel  harder  than  water  at  160°.  Sperm  and  linseed  oils, 
however,  at  all  temperatures  between  32°  and  250°  F.,  act  about  the  same 
as  distilled  water  at  160°.  The  influence  of  the  bath  depends  upon  its 
nature,  its  temperature,  and  its  volume;  or,  in  other  words,  on  its  specific 
heat,  conductivity,  volatility,  and  viscosity.  When  the  bath  is  in  con- 
stant use,  the  first  piece  quenched  will  be  harder  than  the  tenth  or  twen- 
tieth, owing  to  the  rise  in  temperature  of  the  bath.  Therefore,  if  uniform 
results  are  to  be  obtained  in  using  a  water  bath,  it  must  either  be  of  a 
very  large  volume  or  kept  cool  by  some  mechanical  means.  In  other 
words,  the  bath  must  be  maintained  at  a  constant  temperature. 

In  Fig.  120  is  shown  the  effect  of  different  hardening  temperatures 
on  the  tensile  strength  and  elongation  when  quenching  in  different  baths. 
These  tests  were  made  at  the  Watertown  arsenal. 

The  mass  of  the  bath  can  be  made  large,  so  that  no  great  rise  in  tem- 
perature occurs  by  the  continuous  cooling  of  pieces,  or  it  can  be  made 
small,  and  its  rise  in  temperature  used  for  hardening  tools  that  are  to 
remain  fairly  soft.  If  this  temperature  is  properly  regulated,  the  tool 
will  not  have  to  be  reheated  and  tempered  later,  and  cracks  and  fissures 
are  not  as  liable  to  occur.  A  lead  bath,  heated  to  the  proper  temperature, 
is  sometimes  used  for  the  first  quenching.  Another  way  of  arriving  at 
the  same  results  would  be  to  use  the  double  bath  for  quenching,  that  is, 
to  have  one  bath  of  some  product  similar  to  salt,  which  fuses  at  575°  F. 
Quench  the  piece  in  that  until  it  has  reached  its  temperature,  after  which 
it  can  be  quenched  in  a  cold  bath  or  cooled  in  the  air. 


HARDENING   STEEL 


201 


The  specific  heat  of  the  bath  is  an  important  factor,  as  the  more  rapid 
the  cooling  from  1650°  to  200°  F.,  the  more  effective  will  be  the  hardening 
process.  A  bath  that  consists  of  a  liquid  which  volatilizes  easily  at  the 
highest  temperature  it  reaches,  from  plunging  the  metal  into  it,  forms  a 
space  around  the  steel  that  is  filled  with  vapor,  and  this  retards  the  fur- 
ther cooling  action  of  the  liquid.  The  motion  of  the  bath  will  throw  off 
these  vapors  as  it  brings  the  liquid  in  contact  with  the  metal  and  tends 
to  equalize  the  temperature.  The  agitation  of  the  piece  to  be  hardened 


120.000 


110,000 


100.000 


Chemical  composition  -  Carbon  .20,  Manganese. 58,  Silicon  .015,   Phosporus  .017. 


10,000 


12345 
Elongation  -  percent. 


7         8         9        10        11        12        13       14       15       16 


FIG.  120.  —  Effect  of  heat  and  mechanical  treatment  on  the  tensile  stress  and  elongation. 


will  give  better  results  than  trusting  to  the  motion  of  the  bath,  as  it  is 
more  energetic  in  distributing  the  vapors. 

The  viscosity  of  the  bath  has  an  influence  on  the  phenomenon  of 
convection,  which  is  the  principal  means  of  the  exchange  of  heat;  tihe  higher 
the  viscosity  the  less  its  hardening  effect. 

The  conductivity  of  the  bath  has  its  effect  on  the  exchange  of  heat 
between  the  piece  to  be  hardened  and  the  bath;  therefore  the  greater  the 
conductivity  the  more  quickly  the  metal  cools. 

As  a  rule  little  account  is  taken  of  the  specific  heat  of  the  bath,  but 
it  is  an  important  factor.  As  soon  as  the  heated  metal  is  plunged  into 


202  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

the  bath,  the  liquid  begins  to  heat.  The  number  of  calories  necessary 
for  raising  the  temperature  of  the  liquid  a  certain  number  of  degrees 
will  be  the  greater  the  higher  the  specific  heat.  Thus  the  cooling  of  the 
metal  will  heat  the  bath  less  the  higher  the  specific  heat  of  the  latter,  and 
consequently  a  bath  is  the  more  active  the  higher  its  specific  heat.  The 
less  rapidly  the  equilibrium  is  established  between  the  hardening  bath 
and  the  metal  quenched  in  it,  the  more  active  will  be  the  bath. 

The  specific  heat  of  mercury  is  much  less  than  that  of  water,  and  the 
cooling  of  quenched  steel  is  three  times  as  rapid  in  water  as  in  mercury. 
The  hardening  effect  is  therefore  much  lower  than  that  of  water,  but 
surface  cracks  and  fissures  are  not  nearly  as  liable  to  occur. 

METHODS  OF  KEEPING  BATHS  COOL 

The  baths,  for  hardening,  that  give  the  best  results  are  those  in  which 
some  means  are  provided  for  keeping  the  liquid  at  an  even  temperature. 
Of  course,  where  but  few  pieces  are  to  be  quenched,  or  a  considerable 
time  elapses  between  the  quenching  of  pieces,  the  bath  will  retain  an 
atmospheric  temperature  from  its  own  natural  radiation.  Where  a  bath 
is  in  continuous  use,  for  quenching  a  large  number  of  pieces  throughout 
the  day,  some  means  must  be  provided  to  keep  the  temperature  of  the 
bath  at  a  low,  even  temperature.  The  hot  pieces  from  the  heating  fur- 
nace will  raise  the  temperature  of  the  bath  many  degrees,  and  the  last 
piece  quenched  will  not  be  nearly  as  hard  as  the  first. 

When  plain  water  is  used  it  is  easy  to  keep  the  bath  cool  by  providing 
it  with  a  pipe  connecting  it  to  the  supply  main  and  an  outlet  into  the 
drain,  and  thus  have  a  steady  flow  through  the  bath.  Where  a  large 
amount  of  work  is  done  and  the  water  is  paid  for  at  meter  rates,  as  in 
cities,  this  might  be  more  expensive  than  having  a  large  tank  at  an  eleva- 
tion above  the  bath  and  a  pump  to  force  the  water  into  it,  thus  using  the 
water  over  and  over  again.  This  flowing  of  the  liquid  would  do  away 
with  the  necessity  of  agitating  the  steel  in  the  bath,  as  when  it  is  of  the 
ordinary  stationary  kind,  owing  to  the  flowing  liquid  carrying  away 
the  coating  of  vapor  which  forms  around  the  piece  and  prevents  its  cooling 
rapidly. 

A  hole  in  the  center  of  the  bottom  with  an  outlet  on  top  is  not  a  very 
good  arrangement,  as  the  cool  current,  striking  the  bottom  side  of  the 
piece,  is  liable  to  cause  it  to  warp.  If  the  cool  liquid  is  taken  in  at  the 
bottom  it  should  be  taken  in  through  several  openings.  A  good  method 
is  to  have  the  inlet  covered  with  a  spherical  piece  of  sheet  metal  punched 
full  of  small  holes  that  would  deliver  the  liquid  in  fine  streams  similar 
to  that  of  a  sprinkling  can.  This  would  send  the  cool  liquid  to  all  parts 
of  the  bath. 


HARDENING  STEEL 


203 


A  still  better  arrangement  would  be  to  have  an  extra  inner  wall  with 
a  large  number  of  fine  holes  punched  in  the  sides  and  solid  at  the  bottom. 
This  would  cause  the  cool  liquid  to  flow  in  from  all  sides,  which  would 
give  the  bath  a  complete  agitation  and  subject  the  pieces  to  less  irregu- 
larity of  temperature,  and  would  therefore  reduce  the  tendency  of  the 
pieces  to  spring  or  warp  from  not  cooling  equally  on  all  sides.  A  variation 


FIG.  121.  —  Water  spray  quenching  bath. 

of  this  is  shown  in  the  spray  bath  in  Fig.  121.  In  this  A  is  a  circular 
gas  pipe,  into  which  is  screwed  the  perforated  upright  pipes  C,  (7,  and 
B  is  the  intake  pipe.  The  water  comes  through  the  fine  holes  in  pipes 
C,  C,  and  forms  a  spray  on  the  lines  D,  D. 

With  liquids,  other  than  water,  this  method  is  not  practical  owing  to 
the  large  volume  of  liquid  needed  for  the  bath,  and  its  consequent  high 
cost.  Then  again  the  losses  from  evaporation  might  be  too  great.  For 


204  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

this  kind  of  bath  a  water-jacketed  receptacle  could  be  used  and  a  steady 
current  of  cold  water  kept  flowing  through  it,  or  the  bath  could  be  fitted 
with  a  coil  of  rope,  over  the  bottom  and  around  the  sides,  through  which 
a  circulation  of  cold  water  could  be  maintained,  and  thus  keep  the  bath 
cool.  Another  method  that  has  been  used  successfully  is  to  blow  fine 
sprays  of  air  through  the  bath  from  the  bottom  similar  to  the  method  used 
in  the  Bessemer  converter  on  molten  steel.  One  way  of  doing  this  is 
shown  in  Fig.  122. 

With  many  classes  of  work  a  bath  whose  liquid  is  stationary  and  has 
no  mechanical  means  of  cooling  can  be  used  by  having  the  volume  of 
the  bath  large  enough  so  that  the  heat  left  by  the  quenching  of  the  pieces 
is  negligible  in  proportion.  Baths  of  this  character  are  sometimes  fitted 
with  conveyors  that  carry  the  work  through  the  bath,  and  out  after  cool- 
ing sufficiently.  Some  of  these  also  carry  the  work  through  a  pickling 
bath  after  it  has  been  quenched. 


FIG.  122.  —  Pipes  for  cooling  a  quenching 
bath. 


ELECTRICAL     HARDENING 

There  is  another  method  of  hardening  that  is  coming  into  use,  and 
promises  some  interesting  developments  in  the  future.  It  consists  of 
connecting  the  piece  of  steel  to  the  positive  and  negative  wires  of  an  elec- 
trical circuit,  and  inserting  it  into  a  quenching  bath.  The  current  is 
then  turned  on  and  controlled  by  a  rheostat,  so  that  the  metal  can  be 
heated  to  the  proper  temperature.  This  takes  but  a  few  seconds,  and 
when  the  correct  temperature  is  reached,  the  current  is  turned  off  and 
the  steel  is  suddenly  cooled  or  quenched  in  the  bath  in  which  it  was 
heated,  without  being  removed.  In  one  case  the  bath  was  made  of  a 
solution  of  carbonate  of  potash  and  water.  The  piece  is  heated  so  quickly 
that  is  does  not  raise  the  temperature  of  the  bath  to  a  degree  that  retards 
the  hardening  effects. 


HARDENING  STEEL  205 

This  process  prevents  the  scaling  or  blistering  of  the  steel,  as  it  is 
not  brought  into  contact  with  the  air  when  hot,  and  hence  oxidization 
cannot  take  place.  It  also  is  capable  of  many  variations,  as  a  piece  can 
be  locally  heated  and  hardened  in  the  bath,  or  annealed  in  spots  by  heating 
it  outside  of  the  bath.  The  piece  can  also  be  placed  on  a  copper  plate 
and  an  electric  arc  used  to  heat  any  desired  portion  of  it.  It  can  then 
be  quenched  to  harden,  or  annealed,  as  desired.  In  drawing  the  temper 
on  the  inside  of  a  hollow  object,  a  rod  can  be  inserted  in  the  hole  and 
this  heated  up  until  the  desired  color  of  the  steel  has  been  reached  and  the 
current  then  turned  off.  By  noting  the  amount  of  current  consumed  on 
a  few  test  pieces,  it  can  be  regulated,  by  means  of  the  rheostat,  so  that 
uniform  results  can  be  obtained  on  any  number  of  pieces.  The  possi- 
bilities that  this  method  suggests  may  make  it  an  important  factor  in 
the  future  in  heat-treating  steels. 

CRACKING   AND   WARPING 

Much  serious  trouble  has  been  caused  by  cracks  and  fissures  that  have 
been  produced  by  the  abrupt  cooling  of  steel.  Many  times  a  piece  sep- 
arates abruptly  from  the  part  quenched.  The  reason  for  this  is  easily 
given,  as  during  the  cooling  different  parts  of  the  steel  are  at  different 
temperatures.  This  is  many  times  caused  by  thick  and  thin  sections  in 
the  same  piece,  but  it  also  occurs  in  pieces  of  an  even  thickness,  owing 
to  the  change  in  temperature  not  taking  place  everywhere  at  the  same 
time.  This  causes  internal  strains,  which  many  times  attain  enormous 
value  and  result  in  the  lessening  of  the  cohesive  force  that  holds  the  mole- 
cules of  the  metal  together.  This  causes  brittleness  and  rupture  at  the 
places  so  affected. 

In  practical  work  the  main  thing  to  keep  in  mind  is  that  these  fissures 
only  occur  in  high-carbon  steel  or  some  of  the  special  alloys.  There  are 
several  ways  of  overcoming  this,  and  the  three  which  are  the  easiest  to 
use  and  most  certain  in  their  results  are  as  follows: 

First .  —  When  a  water-quenching  bath  is  used  it  may  be  covered 
with  from  |  to  1  inch  of  oil,  which  will  reduce  the  rate  of  cooling. 

Second.  —  A  quenching  bath  of  comparatively  small  size  may  be  used, 
in  which  case  the  sudden  cooling  will  be  followed  by  a  slight  tempering 
effect,  caused  by  the  rise  in  temperature  of  the  bath. 

Third.  —  The  piece  may  be  withdrawn  from  the  bath  before  it  is  com- 
pletely cooled.  Uniform  results  are  hard  to  obtain  by  this  last  method, 
owing  to  the  difficulty  of  judging  the  temperature  of  the  metal  when 
withdrawn. 

Warping  may  be  caused  by  several  factors,  the  two  most  important 
of  which  are,  not  having  the  steel  in  a  proper  condition  of  repose  before 


206  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

it  is  hardened,  and  not  putting  the  piece  in  the  quenching  bath  properly. 
As  any  operation  of  working  steel  is  liable  to  set  up  internal  strains  it 
is  always  best  after  rolling,  forging,  or  machining  steel  to  thoroughly 
anneal  the  piece  before  hardening  it.  This  allows  the  metal  to  assume 
its  natural  state  of  repose.  In  the  machining  operations  the  roughing 
cuts  could  be  taken  off,  the  piece  annealed,  then  the  finishing  cuts  could 
be  given  it  and  the  piece  hardened.  This  would  also  make  the  steel 
easier  to  machine,  as  the  metal  is  more  uniform  and  in  its  softest  state. 

There  are  several  rules  that  can  be  followed  in  hardening  a  piece  of 
steel  to  prevent  warping,  and  these  rules  always"  assume  that  the  piece 
has  been  properly  annealed  before  starting  the  hardening  operations. 

First.  —  A  piece  should  never  be  thrown  into  the  bath,  as  by  laying 
on  the  bottom  it  would  be  liable  to  cool  faster  on  one  side  than  the  other 
and  thus  cause  warping. 

Second.  —  The  piece  should  be  agitated,  so  the  bath  will  convey  its 
acquired  heat  to  the  atmosphere,  and  also  destroy  the  coating  of  vapor 
that  is  liable  to  form  on  certain  portions,  and  thus  prevent  its  cooling 
as  rapidly  here  as  in  the  balance  of  the  piece. 

Third.  —  The  liquid  of  the  bath  should  instantaneously  cover  the 
largest  possible  amount  of  the  surface  of  the  piece  when  plunged  into  it. 

Fourth. —  Hollow  pieces,  such  as  spindles,  should  have  the  ends  plugged, 
as  they  could  not  otherwise  be  quenched  vertically  on  account  of  the 
steam  that  would  be  produced  in  the  hole  and  cause  it  to  throw  hot  water. 

Fifth.  —  Pieces  with  thin  and  thick  sections,  or  of  intricate  shapes, 
should  be  immersed  so  the  most  bulky  parts  would  enter  the  bath  first. 

Sixth.  —  To  harden  one  part  of  a  piece  only,  it  should  be  immersed 
so  that  it  hardens  well  beneath  the  heated  part. 

Seventh.  —  Pieces  which  are  very  complicated  should  be  rigged  up 
with  hoops,  clamps,  or  supports  to  prevent  their  warping. 

The  hardening  of  large  pieces  gives  somewhat  different  results  as  the 
transformation  is  not  always  complete,  in  which  case  there  is  a  partial 
return  to  the  normal  stable  state,  that  is,  toward  pearlite.  Thus  a  small 
piece  quenched  from  a  high  temperature  in  cold  water  is  very  hard  and 
quite  brittle,  while  a  large  piece  quenched  at  the  same  temperature  and 
under  the  same  conditions  is  not  quite  as  hard  and  only  slightly  brittle. 
If  the  large  piece  is  examined  with  the  microscope  it  would  indicate  mar- 
tensite  to  be  present  in  the  surface  layer,  while  at  a  certain  distance  below 
the  surface  would  be  seen  troostite  and  sorbite.  This  would  show  that 
the  transformation  was  not  as  complete  as  in  the  small  piece  and  would 
account  for  the  lower  degree  of  hardness  and  brittleness. 

This  might  lead  one  to  suspect  that  the  constituents  in  the  center  of 
a  large  piece  were  the  same  as  in  annealed  steel,  as  the  coefficient  of  expan- 
sion and  the  electrical  resistance  seem  to  be  the  same.  From  this  might 


HARDENING   STEEL 


207 


be  drawn  the  conclusion  that  the  mechanical  properties  of  the  two  steels 
were  not  the  same.  These,  however,  are  not  the  facts  as  the  strengths 
and  hardness  are  but  little  different  from  those  of  the  small  pieces  that 
showed  martensite. 

On  all  steels,  it  is  a  very  good  rule  that  insists  on  a  slow  pre- 
heating of  the  metal  before  it  is  submitted  to  the  high  temperature  of  the 
hardening  furnace.  If  followed,  this  will  prevent,  to  a  large  extent,  the 
checking,  cracking,  warping,  etc.,  that  is  met  with  so  often  in  the  harden- 
ing room.  To  get  the  best  results,  low-carbon  steels  should  consume 


FIG.  123.  —  Tempering  plate  with  sheet 


iron  oven. 


about  one  hour  in  being  heated  up  to  a  temperature  of  not  less  than 
600°  F. ;  high-carbon  steels  should  be  preheated  to  about  800°,  and  some  of 
the  special  alloy  steels,  especially  high-speed  steel,  to  not  less  than  1000°. 
If  even  a  higher  temperature  than  this  is  reached  in  the  slow  heating, 
it  will  benefit  rather  than  harm  the  metal,  although  at  about  these  tem- 
peratures a  transformation  in  the  grain  of  the  metals  takes  place  that 
enables  it  to  be  heated  more  rapidly  without  any  practical  injury  to  the 
steel. 

The  preheating  need  not  be  made  a  matter  of  much  expense  to  a  hard- 
ening room,  as  low  heat  tempering  furnaces  are  nearly  always  available, 


208 


COMPOSITION   AND   HEAT-TREATMENT   OF  STEEL 


or  if  not  ovens  could  be  placed  over  the  high  heat  furnaces.  One  of  the 
simplest  arrangements  for  slowly  preheating  is  the  hot  plate  that  is 
16  X  24  inches  and  covered  with  a  sheet-iron  oven,  as  shown  in  Fig.  123. 
It  has  6  rows  of  30  small  gas  jets  underneath  the  plate,  and  any  desired 
temperature  can  be  attained  in  the  oven.  A  small  muffle  furnace,  similar 
to  that  shown  in  Fig.  124,  is  also  very  useful  for  preheating,  and  this  can 
be  used  for  reheating  carbonized  work.  Both  of  these  furnaces  can  be 
easily  and  successfully  used  for  tempering,  and  thus  the  preheating  not 
made  an  item  of  expense. 


FIG.  124.  —  Muffle  gas  furnace. 

The  principles  and  practices  of  hardening  are  practically  the  same 
for  the  special  alloyed  steels  as  for  the  ordinary  carbon  steels,  except 
that  some  of  the  alloying  materials  alter  the  point  of  transformation. 


HIGH-SPEED    STEELS 

There  is  one  notable  exception  to  this,  however,  and  that  is  in  the 
case  of  high-speed  or  self-hardening  steels.  These  are  made  by  alloying 
with  the  steel,  tungsten,  and  chromium,  or  molybdenum  and  chromium, 
or  all  three.  These  compositions  completely  revolutionize  the  points 
of  transformation.  Chromium,  which  has  a  tendency  to  raise  the  critical 
temperature,  when  added  to  a  tungsten  steel,  in  the  proportions  of  1  or 
2%,  reduces  the  critical  temperature  to  below  that  of  the  atmosphere. 
Tungsten  and  molybdenum  prolong  the  critical  range  of  temperatures 


HARDENING  STEEL 


209 


of  the  steel  on  slow  cooling  so  that  it  begins  at  about  1300°  F.  and  spreads 
out  all  the  way  down  to  600°. 

These  steels  are  heated  to  from  1850°  to  2450°,  and  cgoled  moderately 
fast,  to  give  them  the  property  known  as  "red-hardness."  Sometimes 
they  are  cooled  in  an  air  blast,  and  sometimes  they  are  quenched  in 
various  liquids.  This  treatment  prevents  the  critical  changes  alto- 


FIG.  125.  —  Cylindrical  gas,  hardening  furnace. 

gether,  and  preserves  the  steel  in  the  austenitic  condition.  The  austen- 
itic  condition  is  one  of  hardness  and  toughness,  and  it  is  peculiar  that 
under  this  heat  treatment  the  steel  is  not  transformed  into  the  pearlitic 
condition. 

One  rule  that  has  given  good  results  in  heat-treating  some  high-speed 
steels  is  to  heat  slowly  to  1500°  F.,  then  heat  fast  to  from  1850°  to  2450°; 
after  which  cool  rapidly  in  an  air  blast  to  1550°;  then  cool  either  rapidly 
or  slowly  to  the  temperature  of  the  air. 


210 


COMPOSITION    AND   HEAT-TREATMENT    OF    STEEL 


HARDENING    FURNACES 

The  furnaces  used  for  heating  steel  up  to  the  necessary  temperatures 
for  hardening  should  be  so  arranged  that  the  oxygen  of  the  air  will  not 
attack  the  metal  when  it  is  hot,  as  then  oxygen  has  its  greatest  affinity 
for  iron,  and  will  combine  with  it  to  form  oxides  that  result  in  scale  blis- 
ters, etc.  The  flame  must  therefore  be  a  reducing  one,  that  is,  contain 
a  deficiency  of  oxygen  so"  it  will  not  attack  the  metal,  or  a  retort  for 
holding  the  work  must  be  used,  and  this  heated  from  the  outside  by  flames 
that  are  not  permitted  to  enter  the  retort. 


FIG.  126.  —  Cylindrical  oil,  hardening  furnace. 

Many  furnaces  that  are  suitable  for  hardening  steel  are  shown  in 
Chapter  VIII,  but  there  are  various  other  styles.  On  long  slender  work 
it  is  often  necessary  to  heat  them,  in  a  liquid  or  otherwise,  with  the  ends 
hanging  down,  and  for  that  reason  furnaces  of  the  style  shown  in  Figs. 
125  and  126  are  the  most  suitable.  These  can  be  made  to  use  either 
gas  or  oil  for  fuel/ 

When  it  comes  to  the  high  temperatures  that  are  needed  for  high- 
speed steel,  specially  designed  furnaces  are  the  most  economical.  The 


HARDENING  STEEL 


211 


furnace  shown  in  Fig.  127  is  one  of  these,  and  the  details  of  its  construc- 
tion are  shown  in  Fig.  128.  A  temperature  of  2500°  F.  can  be  attained 
in  20  minutes,  and  maintained  at  that  figure.  The  blast  pressure  gener- 
ally used  is  about  2  pounds  per  square  inch.  Though  usually  confined 
to  small  work,  the  furnace  can  be  used  for  long  articles,  as  an  opening  at 
the  back  allows  for  the  introduction  of  long  bars,  or  drills.  Two  hori- 
zontal burners,  each  conveying  air  and  gas  in  concentric  tubes,  enter 
the  furnace  on  opposite  sides  and  at  different  levels.  By  an  arrange- 
ment of  channels  in  the  lining  of  the  furnace,  the  flame  is  given  a  rotary 


FIG.  127.  —  Wizard    high-speed    steel 
furnace. 

motion,  with  the  result  that  the  whole  of  the  interior  of  the  heating 
chamber  is  filled  with  flame,  which  passes  round  the  circular  walls  of  the 
chamber,  at  a  high  speed,  and  out  through  the  flues  at  the  back.  Hence 
the  products  of  combustion  pass  to  the  exhaust  box,  that  is  located 
under  the  actual  furnace.  Through  this  box  pass  the  pipes  conveying  the 
incoming  gas  and  air,  so  that  a  regenerative  action  is  set  up,  and  as  soon 
as  the  furnace  is  in  blast,  both  the  gas  and  air  are  preheated. 

Another  style  of  high-speed  steel  furnace  is  shown  by  the  vertical 
type  in  Fig.  129.     A  movable  fire-clay  plate,  which  can  be  raised  or  low- 


212  COMPOSITION  AND   HEAT-TREATMENT   OF  STEEL 


FIG.  128.  —  Sectional  view  of  wizard  high-speed  steel  furnace. 


FIG.  129.  —  Vertical    high-speed   steel 
furnace. 


HARDENING   STEEL  213 

ered  by  means  of  a  rack  and  pinion,  is  used  for  inserting  the  work  in  the 
furnace.  When  raised,  it  forms  the  bottom  of  the  furnace,  by  fitting  into 
a  circular  cavity,  and  the  hardener  need  not  stand  in  the  full  glare  of 
the  opened  furnace  while  he  extracts  the  tool.  It  has  the  flame  injected 
into  the  heating  chamber  at  an  angle  so  it  will  be  given  a  rotating  motion 
and  thereby  heat  all  parts  of  the  chamber  uniformly.  As  hot  gases  rise 
and  cold  gases  descend  the  temperature  of  the  furnace  is  not  reduced  as 
much  when  it  is  opened  at  the  bottom  to  insert  the  tools  as  would  be  the 
case  with  a  side  or  top-opened  furnace.  For  this  reason,  also,  the  flame  is 
inserted  near  the  bottom  of  the  furnace.  The  entire  top  is  a  cover  that 
is  made  of  fire-clay  and  held  together  by  a  steel  band,  with  handles  for 
lifting  it  off.  In  its  center  is  a  small  peep-hole  with  a  cover  fitted  in. 


CHAPTER  XI 

TEMPERING  STEEL 

METHODS,  MATERIALS  USED,  AND  RESULTS  OBTAINED 

NEGATIVE  quenching  consists  of  cooling  the  metal  through  the  critical 
zone  at  a  rate  equal  to  or  below  that  which  will  give  to  the  metal  the 
greatest  elongation  when  cold.  This  rate  of  cooling  separates  the  mechan- 
ical results  of  quenching  into  the  two  distinct  divisions  mentioned  farther 
back,  namely,  that  for  giving  a  cutting  edge  to  tools,  and  that  for  increas- 
ing the  static  strengths  and  dynamic  qualities.  It  varies  as  an  inverse 
function  of  the  carbon  content  unless  the  elements  used  in  the  special 
alloys  influence  it. 

Negative  quenching  gives  a  tensile  strength  and  elastic  limit  about 
equal  to  that  obtained  in  annealed  steel,  and  produces  the  highest 
possible  elongation  and  a  high  reduction  of  area.  This  usually  gives  the 
steel  the  highest  obtainable  resistance  to  shocks. 

As  positive  quenching  becomes  more  and  more  pronounced  it  increases 
the  tensile  strength  and  elastic  limit;  at  first  slowly,  then  more  and  more 
rapidly,  and  reduces  the  elongation  and  resistance  to  shock  in  the  same 
ratio.  Thus,  by  variations  in  the  factors  governing  the  activity  of  the 
quenching  bath,  any  steel  may  be  given  its  most  suitable  state  for  any 
given  purpose.  In  fact,  all  possible  methods  of  quenching  are  but  means 
of  varying  the  rate  of  cooling,  and  the  selection  of  the  cooling  mediums 
which  will  give  the  desired  rate  of  cooling  through  each  of  the  critical 
temperature  zones  of  the  metal  in  order  to  give  it  the  desired  properties 
is  the  real  art  of  heat  treatment. 

Tempering  steel,  therefore,  is  to  return  it  in  part  to  a  state  of  molec- 
ular equilibrium  at  atmospheric  temperature  by  relieving  any  strains  in 
the  metal  which  have  been  caused  by  sudden  quenching,  and  to  correct 
any  exaggeration  of  certain  properties  which  have  been  caused  by  the 
hardening  process. 

The  temperature  to  which  a  piece  should  be  raised  for  tempering 
depends  on  the  use  to  which  it  is  to  be  put,  the  condition  in  which  it  has 
been  left  by  quenching,  and  the  composition  of  the  metal.  The  maxi- 
mum temperature  desired  should  only  be  maintained  long  enough  to 
be  sure  that  the  piece  is  evenly  heated.  The  martensite  which  is  retained 

214 


TEMPERING    STEEL  215 

in  steel  by  the  sudden  cooling  has  a  natural  impulse  to  change  into  pearlite. 
By  reheating  slightly  after  hardening  a  certain  amount  of  molecular 
freedom  is  given  and  changes  take  place  that  lessen  the  molecular  rigid- 
ity set  up  by  the  hardening  process.  The  higher  the  temperature  is  car- 
ried in  reheating,  the  more  it  will  lessen  this  molecular  rigidity,  and  the 
more  will  the  martensite  give  way  to  a  pearlitic  formation. 

Steels  heated  to  150°  F.  will  be  slightly  tempered,  but  if  heated  to 
the  temperature  at  which  the  straw  color  is  formed  on  a  brightened 
surface  by  the  appearance  of  an  iron  oxide,  namely  450°,  a  greater  tem- 
pering will  result,  and  the  temperature  at  which  this  oxide  assumes  a 
permanent  blue  color,  namely  575°,  will  effect  a  still  greater  tempering. 
Each  increase  in  this  temperature  of  reheating  reduces  the  hardness  and 
brittleness,  reduces  the  tensile  strength  and  elastic  limit,  and  increases 
the  elongation  as  well  as  the  resistance  to  shocks. 

Steels  that  are  not  exposed  to  shock,  and  require  a  great  hardness  so 
that  a  fine  cutting  edge  can  be  given  them,  such  as  razors,  can  have 
a  marked  degree  of  brittleness.  A  reheating  to  450°  F.  for  tempering  will 
be  the  best  condition  that  such  steel  can  be  given.  Tools  which  have 
to  withstand  violent  shocks  such  as  cold-chisels  and  still  retain  a  good 
cutting  edge  should  be  reheated  to  575°  to  further  remove  some  of  the 
brittleness.  This  will  lessen  the  hardness,  and  consequently  the  cutting 
powers,  but  is  the  lesser  of  the  two  evils.  These  two  cases  might  be  taken 
as  the  two  extremes  of  temper  desired  in  cutting  tools. 

The  temperature  to  which  it  is  best  to  draw  or  temper  tools  is  about 
as  follows: 


430°  F.,  or  a  Faint  Straw  Color: 

Tools  for  Metal  Planers.  Ivory-cutting  Tools. 

Small  Turning  Tools.  Bone-cutting  Tools. 

Hammer  Faces.  Paper  Cutters. 

Steel-engraving  Tools.  Scrapers  for  Brass. 
Wood-engraving  Tools. 

460°  F.,  or  a  Dark  Straw: 

Punches  and  Dies.  Tools  for  Wood  Planers. 

Screw-cutting  Dies.  Inserted  Saw  Teeth. 

Leather-cutting  Dies.  Knife  Blades. 

Wire-drawing  Dies.  Wood-molding  Cutters. 

Taps.  Tools  for  Cutting  Stone. 

Milling  Cutters.  Rock  Drills. 

Metal-boring  Cutters.  Half-round  Bits. 

Reamers.  Chasers. 


216  COMPOSITION  AND   HEAT-TREATMENT  OF  STEEL 

500°  F.,  or  a  Dark  Brown: 

Wood-boring  Cutters.  Flat  Drills. 

Edging  Cutters.  Twist  Drills. 

Hand-plane  Cutters.  Drifts. 

Coopers'  Tools.  Wood  Gouges. 

530°  F.,  or  a  Light  Purple: 

Hack  Saws.  Dental  Instruments. 

Axes.  Surgical  Instruments. 

Wood  Bits  and  Augers.  Springs. 

550°  F.,  or  a  Dark  Purple: 

Cold-chisels  for  Steel.  Needles. 

Chisels  for  Wood.  Gimlets. 

Circular  Saws  for  Metal.  Screw-drivers. 

570°  F.,  or  a  Light  Blue: 

Cold-chisels  for  Iron.  Molding  Cutters  to  be  filed. 

Saws  for  Wood.  Planer  Cutters  to  be  filed. 

The  temperatures  of  the  different  colors  used  for  tempering  are  about 
as  follows: 

Faint  Straw,  430°  F.  Light  Purple,  530°  F. 

Straw,  460°  F.  Dark  Purple,  550°  F. 

Light  Brown,  490°  F.  Light  Blue,  570°  F. 

Dark  Brown,  500°  F.  Dark  Blue,  600°  F. 

Purple  and  Brown,  510°  F.  Blue  Green,  630°  F. 

These  colors  of  steel,  at  a  given  temperature,  cannot  always  be  depended 
upon,  however,  as  the  various  ingredients  that  enter  into  the  composition 
of  different  grades  of  metal  are  liable  to  influence  the  color.  That  the 
carbon  contents  of  steel  has  an  influence  on  the  colors  is  shown  by  the 
samples  in  Fig.  130.  These  pieces  were  carbonized  and  hardened,  then 
tempered  at  various  temperatures,  as  measured  by  a  pyrometer,  and  it 
is  to  be  regretted  that  the  colors  cannot  be  shown,  although  the  contrast 
between  the  low-carbon  center  and  the  high-carbon  outer  shell  can  be 
seen.  Some  of  these  pieces  were  left  rough,  as  they  were  broken  and 
others  were  ground  and  polished  before  hardening. 

The  pieces  A  and  B  are  ^  X  If  inches,  and  A  is  untreated,  while  B 
was  hardened  and  then  drawn  until  the  high-carbon  outer  shell  was  a 
greenish-blue  color.  The  difference  between  the  two  colors  showed  a 
decided  contrast;  C  and  D  were  ground  and  polished  and  then  hardened 


TEMPERING  STEEL  217 

and  drawn  until  the  outer  shell  was  a  dark  blue.  This  left  the  low-carbon 
center  a  dark  brown.  These  pieces  were  f  inch  diameter.  E  was  hard- 
ened and  not  drawn.  This  left  the  shell  a  bright  steel  color,  while  the 
center  was  almost  a  black;  F  was  drawn  to  a  dark  blue,  and  this  left  the 
center  a  dark  brown,  similar  to  the  pieces  C  and  D;  piece  G  was  drawn 
to  a  purple,  and  this  left  the  center  a  yellow  brown  or  dark  straw  color; 
the  H  piece  was  drawn  to  a  dark  brown  in  the  shell,  which  left  the  center  a 
light  straw  color;  L  was  drawn  to  a  full  purple,  which  left  the  center  a 
spotted  red  brown;  M  was  drawn  to  a  full  blue  in  the  shell,  and  this  left 
the  center  a  brown  purple;  J  was  drawn  to  a  dark  blue,  which  left  the 
center  a  dark  brown,  while  piece  K  was  hardened  and  drawn  to  a  purplish 
blue,  and  this  left  the  center  a  light  brown.  Pieces  7,  N,  P,  and  0  were 
drawn  to  a  dark  blue  on  the  high-carbon  outer  shell,  and  this  left  the 
low-carbon  center  a  dark  brown. 


FIG.  130.  —  Carbonized  steel  after  being  hardened  and  drawn  to  color. 

While  the  hardening  of  steel  by  colors  has  been  successfully  done 
in  the  past,  and  will  be  done  many  times  in  the  future,  these  pieces  would 
seem  to  make  it  imperative  for  the  hardener  to  test  a  sample  piece  from 
each  lot  of  steel  before  attempting  to  harden  it  by  color.  A  much  better 
way,  however,  would  be  to  use  a  pyrometer  for  measuring  the  temper- 
atures as,  if  the  pyrometer  is  kept  in  order,  a  positive  knowledge  of  the 
temperature  at  which  the  metal  is  treated  can  be  instantly  obtained, 
and  the  differences  in  the  light  in  the  shop  or  even  in  color-blindness  will 
not  affect  the  hardener. 

Steels  that  are  used  in  the  building  of  machinery,  as  a  rule,  have  the 
temper  drawn  much  more  than  this,  and  the  variation  in  temper  is  only 
limited  by  the  work  that  the  parts  have  to  do,  the  composition  of  the 
metal,  and  the  different  degrees  of  temper  which  steel  can  be  given.  Leaf 
springs,  such  as  carriage  springs,  are  usually  reheated  to  about  800°  F. 


218 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


Gears  which  are  in  constant  mesh  without  any  undue  pressure  will 
give  the  best  results  as  to  wear,  strengths,  and  resistance  to  shocks 
if  reheated  to  about  675°.  Crank-shafts  on  internal-combustion  engines 


FIG.  131.  —  Spring  deflections.     Comparative  tests. 


have  to  withstand  considerable  torsion,  vibrational  strains,  and  im- 
pact stresses  and  seem  to  stand  the  work  best  when  reheated  to 
about  1000°. 

Fig.   131  and  132  show  the  effect  of  the  above  heat  treatment  for 


TEMPERING  STEEL 


219 


springs  on  two  kinds  of  steel  which  might  be  said  to  show  the  two  extremes 
in  deflection,  fiber  stress,  and  their  resultant  permanent  set.  In  Fig. 
131  the  elastic  limit  was  reached  on  the  second  test.  This  for  the  vana- 
dium steels  was  85,000  pounds,  or  234,500  pounds  fiber  stress  with  a  per- 
manent set  of  0.48  inch.  In  the  carbon  steels  it  was  65,000,  or  180,000 
pounds  fiber  stress  with  a  permanent  set  of  1.12  inches.  The  carbon  steel 


2.0  1.5  1.0  .5 

FIG.  132.  —  Comparative  tranverse  tests. 

took  an  additional  set  of  0.26  inch  on  the  third  test  and  broke  on  the 
fourth  in  the  center.  The  third  test  was  repeated  three  times  on  the 
vanadium  steel  without  any  change  in  recorded  hights.  The  tests  were 
made  by  the  American  Vanadium  Company. 

The  changes  that  can  be  made  in  the  strengths  of  steel  are  very  for- 
cibly shown  in  the  following  Table  No.  2,  which  explains  itself: 


220 


COMPOSITION    AND    HEAT-TREATMENT   OF    STEEL 


TABLE   No.   2 


Tensile  Strength 
Lib.  per  Sq.  In. 

Elastic  Limit 
Lb.  per  Sq.  In. 

Elongation  in 
2  In.,  Per  Cent, 

Reduction  of 
Area,  Per  Cent 

Annealed  at  1475  degrees  

87,640 

64,400 

29 

59 

125,000 

103,000 

21 

56 

127,800 

110,100 

20 

58 

Hardened  at  1650  degrees,  oil 

130,500 

124,000 

17 

62 

tempered  at  varying  temper-  • 
atures                  

138,000 
147,000 

127,500 
140,750 

18 
17 

65 
57 

212,000 

200,000 

12 

51 

232,750 

224,000 

11 

39 

TEMPERING    EQUIPMENT 

The  furnaces  used  are  sometimes  the  same  as  those  used  in  hardening. 
But  furnaces  that  will  permit  of  maintaining  a  constant  temperature 
with  appliances  for  measuring  the  heat  so  the  correct  temperature  can 
be  attained  are  the  best  kind.  Thus,  wherever  possible  it  is  best  to  have 
furnaces  that  are  designed  especially  for  tempering.  These  can  be  built 
cheaper  than  hardening  and  annealing  furnaces,  as  it  is  not  necessary 
to  construct  them  so  they  will  withstand  the  high  heats  used  in  hardening, 
and  special  appliances  can  be  attached  that  are  not  needed  on  the  harden- 
ening  or  annealing  furnaces. 

The  oven  gas  furnace  shown  in  Fig.  133  is  a  very  handy  one  in  which 
to  temper  work,  and  oil  fuel  can  be  used  on  this  style  of  furnace  if  desired. 
The  hot  plate  with  a  sheet  metal  oven,  that  is  shown  in  Fig.  123,  is  also 
very  useful  for  tempering.  Another  type  of  the  gas  furnace  for  temper- 
ing is  shown  in  Fig.  134.  This  is  very  useful  for  small  work  which  is 
inserted  through  the  opening  S  into  the  drum  D,  and  the  door  E  closed. 
The  drum  is  then  rotated  by  a  gear  and  worm  on  shaft  N,  and  the  work 
tumbled  so  all  the  pieces  will  be  uniform  in  temper  and  heated  on  all 
sides.  Drum  D  can  be  pulled  out  of  the  furnace  by  handle  H ,  to  empty 
out  the  work  when  it  is  finished.  The  heat  can  be  accurately  controlled 
at  the  desired  temperature  by  gas  valve  G,  and  air  valve  A,  and  reference 
to  the  thermometer  T. 

Lead  baths  are  used  a  great  deal,  as  it  is  easy  to  heat  these  to  a  certain 
temperature  and  hold  them  at  a  constant  temperature  for  any  length 
of  time.  With  this  the  bath  is  heated  to  the  temperature  at  which  the 


TEMPERING    STEEL 


221 


steel  needs  to  be  tempered  or  drawn,  the  piece  is  placed  in  the  bath  and 
allowed  to  remain  until  it  has  attained  the  temperature  of  the  bath,  and 
it  is  then  taken  out  and  cooled.  One  of  the  simpler  gas-heated  lead  baths 
is  shown  in  Fig.  135.  These,  however,  can  be  heated  with  coal,  coke, 


FIG.  133.  —  Oven  furnace  with  gas  for  fuel. 


oil,  or  any  other  fuel  as  well,  and  they  should  be  supplied  with  a  hood 
that  is  piped  to  the  outside,  as  any  fumes  that  may  arise  from  the  molten 
lead  are  injurious. 

As  the  pure  lead  melts  at  about  620°  F.,  it  is  necessary  to  mix  it  with 
some  other  metal  to  get  the  lower  tempering  temperatures.  Tin  is  the 
most  often  used  for  this  purpose,  as  it  lowers  the  melting  temperature 
sufficiently,  and  is  a  comparatively  cheap  metal.  As  low  as  360°  F.  for 
the  melting  point  can  be  obtained  by  combining  these  two  metals.  The 
alloys  that  will  melt  at  given  temperatures  are  as  follows: 


222  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 


FIG.  134.  —  Revolving  drum  tempering  furnace. 


TEMPERING  STEEL 


223 


200  parts 
100  parts 
75  parts 
60  parts 
48  parts 
39  parts 
33  parts 
28  parts 
24  parts 
21  parts 
19  parts 
17  parts 
16  parts 
15  parts 
14  parts 


Pure  Lead  melts  at  619°  F. 

Lead  and  8  parts  Tin  melt  at 560° 

Lead  and  8  parts  Tin  melt  at 550° 

Lead  and  8  parts  Tin  melt  at   540° 

Lead  and  8  parts  Tin  melt  at   530° 

Lead  and  8  parts  Tin  melt  at   520° 

Lead  and  8  parts  Tin  melt  at 510° 

Lead  and  8  parts  Tin  melt  at 500° 

Lead  and  8  parts  Tin  melt  at   490° 

Lead  and  8  parts  Tin  melt  at .480° 

Lead  and  8  parts  Tin  melt  at   470° 

Lead  and  8  parts  Tin  melt  at  460° 

Lead  and  8  parts  Tin  melt  at   450° 

Lead  and  8  parts  Tin  melt  at   440° 

Lead  and  8  parts  Tin  melt  at   430° 

Lead  and  8  parts  Tin  melt  at   420° 


I) 


H 


FIG.  135.  —  Gas-heated  lead  bath. 

Oil  baths  are  also  used  quite  extensively  for  tempering,  and  like  the 
others  the  bath  should  be  maintained  at  the  temperatures  to  which  it 
is  desired  to  draw  the  temper,  and  the  work  immersed  until  it  has  attained 
the  temperature  of  the  bath  and  then  taken  out  to  cool  in  the  air.  One 
of  the  best  oil  bath  furnaces  is  that  shown  in  Fig.  136,  but  equally  good 


224 


COMPOSITION  AND   HEAT-TREATMENT   OF  STEEL 


results  are  obtained  with  oil-fired  or  electrically  heated  baths.  The  tem- 
perature can  be  easily  controlled  by  means  of  the  gas  and  air  valves, 
as  in  the  other  furnaces  shown,  by  using  the  high  temperature  thermom- 
eter for  a  guide.  The  wire  basket  shown  in  front  of  the  furnace  is  to 
hold  the  work  so  it  can  be  easily  removed  from  the  oil. 

Temperatures  of  600°  F.  can  be  easily  obtained  and  maintained 
in  the  oil  baths  with  the  ordinary  oils,  but  for  temperatures  that  are  much 
higher  than  this  other  materials  should  be  used.  Some  of  the  tallows 


FIG.  136.  —  Gas  heated  oil  bath. 

can  be  successfully  worked  at  temperatures  as  high  as  800°.  Steel  is 
not  injured  by  soaking  in  the  oil  for  an  indefinite  time,  provided  the 
desired  temperature  for  tempering  has  not  been  exceeded.  This  makes 
it  possible  to  temper  large  and  small  pieces  at  the  same  time,  as  while 
the  large  pieces  are  lying  in  the  bath  to  thoroughly  absorb  the  heat  in 
all  their  parts,  the  smaller  pieces  can  be  tempered.  It  is  always  best  to 
slowly  preheat  the  work  to  from  300°  to  400°  before  submitting  it  to  the 
tempering  bath,  as  this  allows  the  molecules  of  the  metal  to  readjust 
themselves  more  thoroughly  than  if  the  piece  is  plunged  immediately 
into  the  tempering  bath. 

The  electrically  heated  oil  bath  is  doubtless  the  best,  as  by  means 


TEMPERING  STEEL 


225 


of  the  rheostat  the  temperature  is  very  easily  controlled.  When  the 
exact  amount  of  current  that  is  required  to  heat  a  given  oil  up  to  a  given 
temperature  is  known,  the  rheostat  can  be  set  at  this  and  no  further 
attention  paid  to  it  until  the  work  is  ready  to  be  taken  out  of  the  bath. 
When  starting  with  a  cold  bath  no  preheating  of  the  work  is  required, 
as  the  rheostat  can  be  set  and  the  work  heated  up  with  the  oil.  To  main- 
tain a  temperature  of  600°  F.  in  one  style  of  electrical  oil  bath,  it  required 


FIG.  137.  —  Tempering  furnace  with  revolving  retort. 


6  kilowatts  per  hour  for  9  gallons  of  oil,  7.2  kilowatts  for  11  gallons,  and 
12  kilowatts  for  20  gallons. 

Salt  baths  are  sometimes  used  where  the  drawing  temperature  desired 
is  575°  F.  Salt  fuses  at  this  point,  and  a  certainty  of  obtaining  this  tem- 
perature in  the  steel  is  assured.  In  using  this  the  salt  is  heated  to  700° 
or  750°,  and  the  steel  placed  in  the  bath.  When  this  is  done  the  cold 
metal  will  cause  the  salt  which  surrounds  it  to  solidify  and  plainly  show 
a  white  crust  around  it.  When  the  steel  has  attained  a  temperature 


226  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

of  575°  the  white  crust  will  disappear  as  the  salt  which  made  it  has  melted 
and  mixed  with  the  rest  of  the  bath.  This  clearly  shows  that  it  is  time 
to  take  the  piece  out  of  the  bath  and  allow  it  to  cool.  This  method  can 
be  used  for  tempering  above  575°  and  below  900°,  but  is  not  practical 
for  higher  or  lower  temperatures  owing  to  the  alteration  in  the  salt  of 
which  it  is  composed. 

Another  method  that  is  used  considerably  on  some  classes  of  work 
is  sand  tempering.  This  consists  of  covering  the  work  with  sand,  and 
heating  both  up  at  the  same  time.  Clean  and  well-dried  sand  is  some- 
times used  in  a  pan,  and  the  metal  heated  up  in  it  over  a  fire.  Some 
special  gas  furnaces  have  also  been  built  for  sand  tempering  in  which  the 
sand  is  permanently  kept  at  the  required  temperature.  The  work  is 
placed  in  this  until  it  has  thoroughly  attained  the  temperature  of  the 
sand,  and  then  cooled  in  the  air.  Continuous  operating  automatic  gas 
furnaces  have  also  been  made  for  sand  tempering.  In  these  the  work 
and  sand  travels  through  the  furnace,  from  one  end  to  the  other,  by  the 
aid  of  a  worm.  The  work  is  then  dumped  out,  while  the  sand  is  brought 
back  to  the  other  end,  inside  of  the  furnace,  by  means  of  a  second  worm. 

A  gas  furnace,  with  a  revolving  retort,  that  is  used  for  tempering  is 
shown  in  Fig.  137.  The  outer  shell  of  the  furnace  is  lined  with  fire- 
brick, and  this  is  heated  by  the  gas.  The  round  retort,  the  opening  of 
which  is  shown  at  the  end,  is  placed  inside  of  the  outer  shell,  and  revolves 
on  4  wheels,  two  of  which  are  at  each  end  of  the  furnace.  It  is  revolved 
by  means  of  bevel  gears,  sprockets  and  chains,  and  a  pulley  and  belt. 
The  whole  is  mounted  on  trunnions,  and  can  be  tilted  to  any  angle  so 
the  work  will  travel  through  the  furnace  automatically.  This  furnace 
is  also  used  to  give  metal  parts  a  gun-metal  finish.  This  color  can  only 
be  given  to  pieces  that  will  stand  tempering  to  600°  F.,  as  it  takes  that 
temperature  to  put  the  color  on  the  metal;  this  being  done  by  means  of 
charred  bone  and  chemicals. 


CHAPTER  XII 
CARBONIZING 

METHODS  AND  MATERIALS  USED  —  EFFECT  OF  ALLOYING  MATERIALS  AND 

HEAT  TREATMENT 

MANY  of  the  steels  that  give  very  high  figures  in  their  strength 
tests  are  made  hard  enough  to  resist  wear  for  such  parts  of  machinery 
as  gears,  cams,  ball  races,  etc.,  by  hardening  and  tempering;  but  when 
the  proper  degree  of  hardness  is  obtained  to  reduce  wear  to  a  minimum, 
they  are  too  brittle  to  withstand  shock  strains. 

For  this  reason  case-hardening,  carbonizing,  or,  as  it  is  called  in  Europe, 
"cementation,"  is  resorted  to,  as  by  this  process  the  outer  shell  can  be 
made  hard  enough  to  resist  wear,  and  the  core  of  the  piece  can  be  left 
soft  enough  to  withstand  the  shock  strains  to  which  it  is  subjected.  By 
this  method  gears  can  be  made  from  some  of  the  special  alloy  steels  that 
will  reduce  the  wear  to  a  point  that  would  have  been  considered  impos- 
sible a  few  years  ago,  and  at  the  same  time  resist  shock  to  such  an  extent 
that  it  is  very  difficult  to  break  out  a  tooth  with  a  sledge  hammer. 

Several  methods  different  from  the  old  established  one  of  packing 
the  metal  in  a  box  filled  with  some  carbonizing  material,  and  then  sub- 
jecting it  to  heat,  have  been  devised  in  the  last  few  years.  Among  them 
might  be  mentioned  the  Harveyizing  process  which  is  especially  appli- 
cable to  armor  plate.  This  in  turn  has  been  followed  by  an  electrical 
and  a  gas  process,  which  claim  to  be  great  improvements  over  the  Har- 
veyizing process.  Very  recently  another  process  has  been  invented  which 
uses  gas  for  carbonizing  in  a  specially  constructed  furnace.  This  is  very 
useful  for  carbonizing  small  work. 

The  Harveyizing  process  uses  a  layer  of  charcoal  between  two  plates 
which  are  heated  in  a  pit  furnace  by  producer  gas.  The  weight  of  the 
upper  plate  brings  the  charcoal  in  close  contact  with  the  surfaces  and  facil- 
itates the  soaking  in  of  the  carbon. 

This  process  has  been  a  great  success,  but  it  also  has  its  faults,  as  the 
carbon  soaks  in  to  a  good  depth  in  some  places,  while  at  other  places, 
sometimes  only  a  foot  away,  the  carbon  will  not  be  so  deep,  so  that  when 
tested  a  shot  will  glance  off  from  one  spot,  and  when  it  hits  a  short  dis- 

227 


228  COMPOSITION    AND   HEAT-TREATMENT   OF    STEEL 

tance  from  this  will  tear  a  great  hole  in  the  plate.  Then  again  the  Har- 
veyizing  process  is  not  suitable  for  small  work. 

Electricity  has  also  been  used  in  a  like  manner  to  gas  in  the  Harvey- 
izing  process.  That  is,  armor  plate  has  been  covered  with  a  layer  of 
ground  bone,  the  whole  enclosed  and  a  current  of  electricity  turned  on 
to  heat  the  bone  and  metal  so  that  the  carbon  will  combine  with  the 
steel  in  a  surface  layer  of  desired  depth,  and  it  is  claimed  for  this  process 
that  the  depth  can  be  regulated,  and  the  carbonization  is  even  over  the 
entire  surface. 

As  these  two  processes  are  only  used  on  armor  plate  or  other  large 
work  of  a  similar  character,  and  are  too  expensive  in  their  installation 
to  be  made  applicable  to  parts  of  machinery,  or  tools,  they  will  not  be 
gone  into  in  detail  here. 

The  Krupp  process  is  similar  to  the  above  two  in  the  kind  of  work 
it  operates  on,  and  differs  from  Harveyizing  in  that  it  uses  a  gaseous  hydro- 
carbon to  replace  the  bed  of  charcoal.  This  also  is  foreign  to  the  subject, 
but  the  gas  it  uses  is  practically  the  same  as  that  used  in  the  furnace  for 
carbonizing  with  gas,  which  will  be  described  later. 


FACTORS   GOVERNING   CARBONIZING 

The  result  of  the  carbonizing  operation  is  determined  by  five  factors, 
which  are  as  follows:  First,  the  nature  of  the  steel;  second,  the  nature  of 
the  carbonizing  material;  third,  the  temperature  of  the  carbonizing  fur- 
nace; fourth,  the  time  the  piece  is  submitted  to  the  carbonizing  process; 
fifth,  the  heat  treatment  which  follows  carbonizing. 

The  nature  of  the  steel  has  no  influence  on  the  speed  of  penetration 
of  the  carbon,  but  has  an  influence  on  the  final  result  of  the  operation. 
If  steel  is  used  that  has  a  carbon  content  up  to  0.56%,  the  rate  of  pene- 
tration in  carbonizing  is  constant;  but  the  higher  the  carbon  content, 
in  the  core,  the  more  brittle  it  becomes  by  prolonged  annealing  after 
carbonizing.  Therefore  it  is  necessary  that  the  carbon  content  should 
be  low  in  the  core,  and  for  this  reason  a  preference  is  given  to  steels  con- 
taining from  0.12  to  0.15%  of  carbon  for  carbonizing  or  case-hardening 
purposes.  Some,  however,  prefer  a  steel  containing  from  0.20  to  0.22% 
carbon,  owing  to  its  being  more  easily  worked  with  machine  tools;  but 
the  results  will  not  be  as  good  as  with  a  steel  containing  a  maximum  of 
0.15%  carbon.  Greater  strength  and  easier  working  qualities  can  be 
obtained  by  the  addition  of  such  alloys  as  chromium,  vanadium,  titanium, 
nickel,  etc. 

MANGANESE.  —  It  is  also  very  important  that  the  manganese  content 
of  carbonizing  steels  be  kept  low.  This  should  never  exceed  0.35%, 


CARBONIZING  229 

as  manganese  has  a  tendency  to  render  the  hardened  and  carbonized 
surface  brittle,  thus  making  it  liable  to  chip  and  break  at  the  least  shock. 
Thus  manganese  is  usually  kept  down  to  0.20%,  and  seldom  exceeds 
0.25%. 

CHROMIUM.  —  While  chromium  has  a  tendency  to  produce  a  mineral 
hardness  in  steel,  it  prevents  the  development  of  the  crystalline  struc- 
ture under  heat  treatment,  thus  refining  the  grain  and  making  it  better 
able  to  withstand  shocks.  Therefore  chromium  added  in  small  per- 
centages makes  steels  for  carbonizing  more  homogeneous,  and  imparts 
to  them  greater  strengths  and  wearing  qualities.  Chromium,  however, 
produces  steels  that  are  very  difficult  to  machine;  it  is  therefore  com- 
bined with  other  ingredients  which  offset  this,  except  for  such  uses  as 
armor  plate. 

VANADIUM,  used  in  homeopathic  doses,  overcomes  this  difficulty  of 
machining  chrome  steels  to  such  an  extent  that  it  is  claimed  that  a 
steel  containing  1%  chromium  and  from  0.16  to  0.18%  vanadium,  can 
be  forged  and  machined  as  easily  as  a  0.40%  carbon  steel.  Vanadium 
also  produces  high  dynamic  strengths,  which  gives  the  core  of  carbonized 
steels  a  high  resistance  to  shocks. 

TITANIUM  produces  practically  the  same  results  as  vanadium  in 
steels  for  carbonizing,  and  is  usually  used  in  percentages  of  from  0.40 
to  0.50. 

NICKEL,  added  to  ordinary  carbonizing  steel  in  comparatively 
small  percentages,  obviates  the  brittleness  which  is  usually  produced  by 
carbonizing,  and  makes  it  more  homogeneous,  the  pearlite  being  dis- 
tributed much  better.  With  2%  of  nickel,  the  steel  is  increased  in 
strength;  in  some  cases  this  strength  is  nearly  double  that  of  the  ordi- 
nary carbonizing  steel,  but  2%  nickel  steel  means  nothing  unless  the 
carbon  is  of  the  proper  percentages.  When  it  is,  it  makes  one  of  the 
best  of  steels,  when  carbonized  and  tempered,  for  such  parts  as  shafts, 
ball  races,  gears,  etc.  It  should  therefore  be  used  wherever  the  2J  cents 
difference  in  price  does  not  make  it  prohibitive,  except  where  the 
higher  price  alloy  steels  are  demanded,  owing  to  their  greater  strength 
and  wearing  qualities. 

A  2%  nickel  steel  carbonized  so  that  the  surface  layer  contains  about 
1%  of  carbon  will  be  pearlitic,  but  a  7%  nickel  steel  will  show  a  surface 
layer  that  is  martensitic,  with  a  pearlitic  core.  Martensite  being  a  con- 
stituent of  quenched  steel,  a  7%  nickel  steel  carbonized  so  the  surface 
layer  contains  1%  of  carbon  has  the  came  constitution  as  an  ordinary 
carbonizing  steel  that  has  been  carbonized  and  hardened,  that  is,  a  pearl- 
itic core  and  a  martensitic  outer  shell.  This  martensite  should  become 
denser  and  denser  as  it  approaches  the  outer  surface.  This  will  give 


230 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


high  strengths,  and  the  outer  layer  will  readily  polish  without  wear,  thus 
giving  it  valuable  wearing  qualities. 

This  simplifies  the  processes  of  carbonizing,  owing  to  its  doing  away 
with  the  hardening  processes  afterward,  but  the  carbonizing  and  the 
cooling  afterward  must  be  carefully  done  in  order  to  get  good  results 
from  this  process.  If,  however,  the  proper  carbonizing  materials  are 
used,  the  heat  of  the  furnace  regulated  so  that  it  remains  steady  and  at 
the  proper  temperature,  and  the  piece  not  cooled  too  quickly,  a  saving 
in  time  and  expense  can  be  made  with  this  process  of  carbonizing,  when 
this  grade  of  steel  is  suitable. 

The  influence  of  the  different  elements  on  the  speed  of  penetration 
of  the  carbon,  when  carbonizing  steels  containing  the  same  amount  of 
carbon  and  different  percentages  of  manganese,  chromium,  nickel,  tung- 
sten, silicon,  titanium,  molybdenum,  and  aluminum,  is  shown  by  Table  3. 

TABLE  3. — PENETRATION   OP  CARBON  PER  HOUR 


Component  of  Alloys 

Speed  of  Pene- 
tration Per 
Hr.  in  Inches 

Component  of  Alloys 

Speed  of  Pene- 
tration Per 
Hr.  in  Inches 

0.5  per  cent,  manganese.  .    .  . 

0.043 

1.0  per  cent,  silicon  

0.020 

1.0  per  cent,  manganese 

0.047 

2.0  per  cent,  silicon 

0016 

1.0  per  cent,  chromium  
2.0  per  cent,  chromium  .    .  . 

0.039 
0.043 

5.0  per  cent,  silicon  
1.0  per  cent,  titanium   .... 

0.000 
0.032 

2  0  per  cent,  nickel 

0.028 

2.0  per  cent,  titanium     .  .  . 

0.028 

5.0  per  cent,  nickel  
0.5  per  cent,  tungsten.  .  . 

0.020 
0.035 

1.0  per  cent,  molybdenum. 
2.0  per  cent,  molybdenum. 

0.036 
0.043 

1  0  per  cent,  tungsten. 

0.036 

1.0  per  cent,  aluminum. 

0.016 

2.0  per  cent,  tungsten  
0.5  per  cent,  silicon     .      .  . 

0.047 
0.024 

3.0  per  cent,  aluminum.  .  .  . 

0.008 

The  rate  of  penetration  for  ordinary  carbonizing  steel  under  the  same 
conditions  would  have  been  0.035  inch.  Thus  it  will  be  seen  that  man- 
ganese, chromium,  tungsten,  and  molybdenum  increase  the  rate  of  pene- 
tration. These  seem  to  exist  in  the  state  of  a  double  carbide  and  release 
a  part  of  the  cementite  iron. 

Nickel,  silicon,  titanium,  and  aluminum  retard  the  rate  of  penetra- 
tion —  5%  of  silicon  reducing  it  to  zero  —  and  these  exist  in  the  state 
of  solution  in  the  iron.  The  titanium  steel,  however,  has  more  titanium 
in  it  than  should  be  present  in  carbonizing  steel,  and  if  this  were  reduced 
to  0.50%  the  results  might  be  different.  As  it  is,  the  1%  of  titanium  only 
very  slightly  retarded  the  penetration. 

As  a  general  rule  the  alloyed  steels  that  give  the  best  results  in  anneal- 
ing, hardening,  and  tempering  are  not  the  best  for  carbonizing;  for  this 


CARBONIZING  231 

reason  most  of  these  alloyed  steels  are  made  in  a  special  grade  for  car- 
bonizing. As  an  illustration  of  this,  vanadium  steel  that  gives  the  best 
results  for  crank-shafts,  transmission  shafts,  connecting  rods,  and  other 
moving  engine  parts  is  composed  of  0.25  to  0.30%  carbon,  0.40  to  0.50% 
manganese,  1%  chromium,  and  0.16  to  0.18%  vanadium,  while  the  best 
carbonizing  steel  has  from  0.12  to  0.15%  carbon,  0.20%  manganese, 
0.30%  chromium,  and  0.12%  vanadium. 


CARBONIZING   MATERIALS 

The  nature  of  the  carbonizing  materials  has  an  influence  on  the  speed 
of  penetration,  and  it  is  very  essential  that  the  materials  be  of  a  known 
chemical  composition,  as  this  is  the  only  way  to  obtain  like  results  on 
the  same  steel  at  all  times. 

These  materials  or  cements  are  manufactured  in  many  special  and 
patented  preparations.  The  following  materials  are  used  for  carbonizing 
purposes:  Powdered  bone,  wood  charcoal,  charred  sugar,  charred  leather, 
cyanide  of  potassium,  ferrocyanide  of  potassium,  acid  cleaned  animal 
black,  anthracite,  graphite,  horn,  acetylene,  petroleum  gas,  naphtha, 
carbon  monoxide,  illuminating  gas,  and  gasoline.  In  addition  such  ma- 
terials as  black  oxide  of  manganese,  barium  carbonate,  ammonia,  and 
others  are  used  in  mixture  with  the  preceding  substances. 

Such  materials  as  bone  and  leather  should  not  be  used  alone  as  it  is 
impossible  to  obtain  definite  results  from  them,  owing  to  the  changeabil- 
ity of  their  chemical  composition  when  subjected  to  a  temperature  high 
enough  for  carbonizing. 

Wood  charcoal  is  very  largely  used  in  carbonizing  steels,  but  the 
value  of  this  material  varies  with  the  wood  used,  the  method  employed 
in  making  the  charcoal,  and  other  factors.  Used  alone  it  gives  the  normal 
rate  of  penetration  for  the  first  hour,  but  after  that  the  rate  gradually 
decreases  until  at  eight  hours  it  gives  the  lowest  rate  of  penetration  of 
any  of  the  carbonizing  materials. 

The  best  wood  charcoal  is  that  made  from  hickory.  This  is  due  to 
the  fact  that  this  charcoal  contains  a  relatively  high  percentage  of  car- 
bonate of  potassium,  and  this,  in  conjunction  with  the  charcoal  and  the 
nitrogen  of  the  air,  in  the  carbonizing  box,  is  capable  of  giving  cyanide 
of  potassium.  Thus,  by  combining  wood  charcoal  and  carbonate  of  potas- 
sium, an  increase  in  the  rate  of  penetration  can  be  obtained;  but  this  speed 
decreases  with  time,  due  to  the  volatilization  of  the  alkaline  cyanides. 
If  a  current  of  ammonia  is  used,  the  rate  of  penetration  becomes  constant, 
as  cyanide  of  ammonium  is  formed.  Therefore  some  consider  the  best 
carbonizing  materials  to  be  the  ones  that  produce  the  most  of  this  sub- 
stance. 


232  COMPOSITION    AND    HEAT-TREATMENT    OF    STEEL 

Powdered  charcoal  and  bone  give  good  results  as  a  carbonizing  material 
and  are  successfully  used  in  carbonizing  nickel-chrome  steel,  by  packing 
it  in  a  cast-iron  pot  and  keeping  this  at  a  temperature  of  about  2000°  F. 
for  four  hours,  and  then  cooling  slowly  before  taking  the  metal  out  of  the 
pot  or  removing  the  cover. 

Pure  carbon,  such  as  that  of  sugar,  does  not  carbonize  in  vacuum; 
therefore  a  carbonizing  material  that  is  simply  composed  of  carbon  can 
only  act  directly  by  solution  of  the  carbon,  starting  with  the  iron  in  con- 
tact with  it.  Thus  sugar  should  be  mixed  with  some  other  material  in 
order  to  obtain  the  best  results  from  carbonization.  Carbonic  oxide, 
giving  2CO  =  C  +  C02,  which  is  formed  by  the  action  of  the  air,  in  the 
carbonizing  box,  on  a  carbonizing  material  that  is  composed  simply  of 
carbon,  may  act;  but  its  action  is  slow,  and  the  carbonic  acid,  CO2,  has  a 
decarbonizing  action. 

Materials  containing  a  cyanide  act  by  means  of  the  cyanogen  radical 
(CN)2.  This  compound  is  decomposed,  giving  up  its  carbon  to  the  steel. 
In  some  cases  a  small  amount  of  cyanide  appears  to  act  as  a  carrier  of  car- 
bon from  some  other  substance  to  the  steel.  Ferro-cyanide  of  potassium 
heated  gives  cyanide,  cyanate  of  potassium,  and  oxide  of  iron.  A  mixture 
of  ferro-cyanide  and  bichromate  of  potash  gives  rise  to  a  new  mixture  of 
cyanide  and  cyanate  diluted  in  a  mass  of  iron  and  chromium  oxide.  Car- 
bonate of  barium,  under  certain  conditions  and  in  the  presence  of  the 
nitrogen  of  the  air,  gives  rise  to  cyanide  of  barium  according  to  the  fol- 
lowing equation:  2N  +  4C  +  CO3Ba  =  (CN)2Ba  +  SCO.  Therefore  it 
acts  by  means  of  cyanide  and  carbonic  oxide. 

Certain  carbonizing  materials  contain  carbonates  that  are  dissociable 
at  the  temperature  of  carbonization,  especially  calcium  carbonate.  In 
the  presence  of  carbon  there  is  formed  carbonic  oxide,  which  carbonizes 
very  slowly. 

Therefore  the  carbonizing  materials  might  be  classed  as  follows:  First, 
cements  which  act  by  means  of  carbonic  oxide;  second,  cements  which 
act  by  means  of  a  cyanide,  such  as  potassium,  barium,  or  ammonium; 
third,  cements  which  act  by  means  of  hydrocarbons.  To  carbonize 
with  the  hydrocarbons,  it  is  necessary  to  generate  the  gases  and  con- 
duct these  to  the  receptacle  in  which  the  work  has  been  placed  in  such 
a  manner  that  they  may  carbonize  the  pieces  before  passing  out  of  the 
vent. 

J.  C.  Olson  and  J.  S.  Weissenback,  at  the  Polytechnic  Institute  in 
Brooklyn,  made  some  tests  on  carbonizing,  with  gases.  They  used  f 


CARBONIZING 


233 


inch  soft  Norwegian  iron  that  contained  0.08%  of  carbon,  and  the  results 
are  best  shown  in  Table  4. 


TABLE   4. —  RESULT   OF  EXPERIMENT  OF   CARBONIZING   STEEL  WITH   GASES 


Test 
Number 

Gas  Used 

Time 
in 
Hours 

Hard- 
ness 

Depth 
of  Case, 
Inches 

Carbon 
Content, 
Per  Cent. 

1 

Illuminating  and  ammonia  (a)  

4 

glass 

0.004 

0.57 

9 

Illuminating  and  ammonia  (b)    . 

4 

glass 

0008 

0  66 

3 

Illuminating  and  ammonia  (c)  

4 

glass 

0.008 

0.91 

4 

Illuminating  

4 

none 

none 

none 

5 

Illuminating  and  ammonia  (a) 

8 

class 

0012 

1  12 

6 

Illuminating  and  ammonia  (6)  

8 

glass 

0.012 

1.16 

7 

Illuminating  and  ammonia  (c)  

8 

glass 

0.012 

1.15 

8 

Carbon  monoxide  and  ammonia  (c)  .  . 

4 

glass 

0.016 

1.45 

9 

Carbon  monoxide  

4 

glass 

0.016 

1.36 

10 

Acetylene  and  ammonia  (c) 

4 

glass 

0012 

098 

11 

Acetylene 

4 

little 

not  well  defined 

041 

12 

Methane  and  ammonia  (c)  

4 

little 

not  well  defined 

0.32 

13 

Methane 

4 

little 

not  well  defined 

0  26 

The  ammonia  was  used  in  different  strengths  a  being  the  weakest 
with  b  twice  the  strength  of  a  and  c  twice  the  strength  of  b. 

From  the  results  shown  in  this  table  the  conclusions  were  drawn 
that  ammonia  gas  facilitates  the  case-hardening  in  all  cases  except  that 
of  carbon  monoxide,  which  seems  to  act  almost  as  well  without  as  with 
ammonia.  Of  the  three  pure  gases  studied,  the  carbonizing  ability  is 
in  the  following  order:  Carbon  monoxide,  acetylene,  methane.  The 
illuminating  gas  not  being  a  pure  gas  and  varying  in  composition  with 
the  different  gas  companies,  it  cannot  be  given  a  fair  comparison  with 
the  other  gases.  With  illuminating  gas  and  the  strongest  ammonia  the 
4-hour  test  showed  a  very  good  percentage  of  carbon,  and  in  the  8-hour 
test  the  percentages  of  carbon  ran  about  equal  in  all  of  the  three  different 
strengths  of  ammonia. 

The  results  obtained  from  carbon  monoxide  show  it  to  be  by  far  the 
best  gas  for  this  purpose,  and  the  difference  in  the  carbon  percentage 
between  carbon  monoxide  alone  and  carbon  monoxide  combined  with 
the  strongest  ammonia  was  so  slight  that  it  does  not  seem  necessary  to 
use  ammonia  with  it.  In  the  case  of  carbon  monoxide  the  gas  was 
freed  from  carbon  dioxide  by  bubbling  through  strong  caustic  potash 
solution  before  entering  the  case-hardening  tube.  Roughly  speaking, 
the  hardening  depth  is  for  the  four  hours  proportional  to  the  time. 

NITROGEN.  —  The  commonly  used  carbonizing  materials  all  contain 


234 


COMPOSITION  AND  HEAT-TREATMENT   OF  STEEL 


nitrogen  in  some  form  or  other,  and  as  the  non-nitrogenous  materials 
cost  from  one  tenth  to  one-twentieth  of  those  containing  nitrogen,  some 
experiments  have  been  made  with  anthracite  and  coke.  After  carbonizing 
the  same  sized  test  pieces  with  these  for  four  hours  at  1650°  F.,  the  pene- 
tration for  the  anthracite  was  0.006  inch,  and  with  the  best  grade  of  hard 
coke  it  was  0.0064  inch.  Charred  leather  under  the  same  conditions  gave 
a  penetration  of  0.062  inch.  As  this  was  in  the  proportions  of  10  to  1 
it  would  lead  to  the  conclusion  that  nitrogen  performs  an  important 
part  in  carbonizing. 

The  effect  of  ammonia  was  also  tried  by  carbonizing  in  a  gas  pipe, 
and  packing  the  work  in  sugar  charcoal  as  the  non-nitrogenous  material. 
Dry  ammonia  was  passed  into  one  end  of  the  gas  pipe,  and  allowed  to 
flow  out  through  a  small  vent  hole  in  the  other  end.  The  results  obtained 
by  carbonizing  for  four  hours  at  1650°  were  0.058  inch  for  the  charred 
sugar  alone,  and  0.070  inch  for  the  charred  sugar  which  had  ammonia 
passing  through  it.  The  non-ammonia  specimen  was  bluish-black  in 
color,  and  when  sawed  appeared  soft,  while  the  ammonia-treated  specimen 
was  of  a  distinct  whitish  luster,  and  appeared  to  have  a  tough  outer  skin 
when  sawed. 

Thus  all  the  evidence  goes  to  prove  that  nitrogen  aids  carbonizing 
in  practical  work,  and  whether  present  in  organic  form  or  as  ammonia  it 
acts  as  a  carrier  of  carbon,  probably  through  the  formation  of  small  traces 
of  cyanides. 

The  speed  of  penetration  caused  by  the  action  of  different  cements 
at  different  temperatures  for  the  same  time,  i.e.,  eight  hours,  is  best  shown 
by  Table  5. 


TABLE   5 


MATERIALS  USED  AND  RATE  OF  PENETRATION  IN  INCHES 

Temperature  in 
Degrees 
Fahrenheit 

Charcoal  60  per 
cent.  +  40  per  cent, 
of  Carbonate  of 

Ferro-cyanide  66 
per  cent.  +  34  per 
cent,  of 

Ferro-cyanide 
Alone 

Powdered  Wood 
Charcoal  Alone 

Barium 

Bichromate 

1300 

1475 

0.020 

0.033 

0.020 

0.020 

1650 

0.088 

0.069 

0.079 

0.048 

1825 

0.128 

0.128 

0.128 

0.098 

2000 

0.177 

0.177 

0.198 

0.138 

The  nature  of  the  carbonizing  materials  has  a  very  pronounced  effect 
on  the  rate  of  carbonization,  or  the  percentage  of  the  carbon  content 
in  the  surface  layer  of  the  piece,  or  both. 


CARBONIZING 


235 


At  the  same  temperature,  i.e.,  1825°  F.,  for  different  lengths  of  time 
and  with  different  cements,  the  rate  of  penetration  obtained  was  according 
to  Table  6. 


TABLE   6 


Length  of 
Time  in 
Hours 

MATERIALS  USED  AND  RATE  OF  PENETRATION  IN  INCHES 

Carbon  60  per 
cent.  +  40  per 
cent,  of  Carbonate 

Ferro-cyanide  66 
per  cent.  +  34 
per  cent,  of 
Bichromate 

Powdered 
Wood 
Charcoal 
Alone 

Charcoal  and 
Carbonate  of 
Potassium 

Unwashed 
Animal 
Black 

1 

0.031 

0.033 

0.028 

0.059 

0.035 

2 

0.039 

0.037 

0.053 

0.078 

0.059 

4 

0.047 

0.049 

0.063 

0.094 

0.088 

6 

0.078 

0.074 

0.072 

0.011 

0.106 

8 

0.118 

0.128 

0.098 

0.138 

0.128 

Eighty  per  cent,  charcoal  +  20%  carbonate  of  barium,  40%  charcoal 
+  60%  carbonate  of  barium,  ferro-cyanide  alone  and  66%  ferro-cyanide 
+  34%  bichromate  were  used  with  practically  the  same  results  for  eight 
hours'  time. 

Another  set  of  tests  was  carried  out  for  a  longer  period  of  time,  with 
other  materials  and  at  a  uniform  temperature  of  1650°  F.,  with  the  results 
given  in  Table  7. 

TABLE   7 


MATERIALS  USED  AND  RATE  OF  PENETRATION  IN  INCHES 


Hours 

Charred 
Leather 

Ground  Wood 
Charcoal 

Barium  Carbonate  and 
Wood  Charcoal 

2 

0.045 

0.028 

0.055 

4 

0.062 

0.042 

0.087 

8 

0.080 

0.062 

0.111 

12 

0.110 

0.070 

0.125 

The  test  bars  in  this  table  were  3  inches  long  and  }  of  an  inch  square. 
The  chemical  composition  of  the  steel  was  as  follows:  Carbon,  0.14%; 
manganese,  0.58%;  silicon,  0.01%;  sulphur,  0.08%,  and  phosphorus, 
0.03%. 

These  tables  show  that  charcoal  when  used  alone  gives  the  slowest 
rate  of  penetration,  but  when  combined  with  other  materials  the  rate 
of  penetration  is  the  highest  of  any  of  the  tests  made.  In  some  cases 
the  rate  of  penetration  of  the  combined  materials  nearly  doubles  that 
of  the  wood  charcoal  alone. 


236  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

EFFECT   OF  TEMPERATURE 

The  degree  of  carburization  of  the  skin  depends  largely  on  the  degree 
of  temperature  maintained  during  the  carbonizing  process;  therefore  it 
is  necessary  that  the  temperature  be  kept  at  a  definite  point  in  the  car- 
bonizing of  steels.  This  can  best  be  done  by  attaching  to  the  furnace 
something  to  gage  the  heat,  such  as  a  pyrometer.  If  the  temperature 
is  too  high,  the  metal  is  liable  to  crystallize  and  the  core  will  rapidly 
become  brittle.  And  if  too  low  the  rate  of  penetration  will  be  low.  The 
temperature  to  which  the  metal  can  be  safely  raised  in  carbonizing  varies 
with  the  kind  of  steel  used.  As  a  general  rule  the  ordinary  carbonizing 
steel  cannot  be  raised  to  a  temperature  in  excess  of  1800°  F.  If  the  original 
carbon  content  is  high,  even  this  temperature  cannot  be  safely  reached, 
while  with  some  of  the  alloy  steels,  such,  for  instance,  as  nickel-chrome 
steel,  a  carbonizing  temperature  of  2000°  can  be  retained  for  four  hours 
without  the  core  crystallizing,  and  the  rate  of  penetration  will  be  reason- 
ably high,  providing,  of  course,  that  the  original  carbon  content  is  low. 

The  temperature,  however,  must  be  kept  above  1300°  F.,  as  ordinarily 
carbonization  cannot  take  place  below  that  point,  although  in  an  experi- 
mental way  steel  has  been  carbonized  at  about  850°  by  using  a  mixture 
of  cyanide  of  potassium,  chlorides  of  the  alkalies,  and  the  alkaline  earths, 
the  latter  being  used  to  lower  the  fusion  point  of  the  cyanide. 

The  percentage  of  carbon  which  is  absorbed  by  the  steel  is  also  affected 
by  the  temperature  as  well  as  by  the  materials  used.  With  a  given  depth 
of  penetration  and  a  given  amount  of  carbon  in  the  carbonizing  material, 
steel  will  absorb  a  greater  percentage  of  carbon  at  a  high  temperature 
than  at  a  low  one. 

HEAT   TREATMENT   AFTER   CARBONIZING 

The  heat  treatment  following  carbonizing  should  be  very  carefully 
done  owing  to  the  fact  that  the  piece  must  have  a  very  hard  outer  sur- 
face to  resist  wear,  and  a  non-brittle  core  that  will  resist  strains;  also, 
some  methods  of  heat-treating  have  a  decarbonizing  effect,  and  some  of 
the  steels  have  a  tendency  to  produce  cracks  or  fissures  and  to  warp. 
Thus  crank-shafts  for  internal-combustion  engines  were  formerly  car- 
bonized and  hardened,  but  owing  to  the  difficulty  of  preventing  cracks  and 
warping  this  practice  has  been  abandoned. 

As  a  general  rule  the  piece  should  be  annealed  after  carburizing.  This 
can  best  be  done  by  leaving  it  packed  in  the  carbonizing  case,  with  the 
cover  fastened  on,  and  allowing  it  to  cool  gradually;  but  if  the  carbonizing 
temperature  is  not  over  1600°  F.,  it  can  be  allowed  to  cool  to  750°,  then 
reheated  to  1400°,  and  quenched  with  good  results.  If  the  carbonizing 
temperature  is  a  high  one,  i.e.,  above  1800°,  the  piece  should  be  allowed 


CARBONIZING  237 

to  cool,  then  reheated  to  1650°,  and  quenched  and  reheated  again  to 
1400°  and  quenched. 

The  reason  for  the  double  quenching  is  that  the  piece  must  be  heated 
to  above  its  point  of  transformation,  i.e.,  1650°,  to  destroy  the  crystal- 
lization and  consequent  brittleness,  which  is  liable  to  be  in  the  core  when 
it  is  carbonized  at  a  high  temperature;  but  this  leaves  the  carbonized 
surface  layer  not  hard  enough  to  resist  wear,  therefore  it  must  be  quenched 
again  at  1400°.  This  point  of  transformation  varies  with  the  different 
components  of  the  high-grade  alloy  steels,  and  this  should  be  ascertained 
before  hardening  the  piece. 

By  quenching  directly  from  the  carbonizing  retort  a  distinct  line 
is  formed  between  the  high-carbon  outer  shell  and  the  low-carbon  cone, 
and  this  is  liable  to  cause  the  metal  to  crack  on  this  line  when  the  work 
is  used  for  parts  similar  to  rollers  in  roller  bearings,  owing  to  the  wearing 
and  crushing  strains  to  which  they  are  submitted,  but  if  the  work  is  prop- 
erly heat-treated  after  carbonizing,  this  distinct  line  is  made  to  disappear, 
and  the  danger  of  the  steels  cracking  there  is  removed. 

Aside  from  the  above  rules,  the  general  rules  should  be  followed  that 
are  laid  down  for  annealing,  hardening,  and  tempering,  in  their  respective 
chapters. 

TIME   OF   EXPOSURE 

The  time  that  the  work  is  submitted  to  carbonizing  is  an  important 
factor,  as  the  regulation  of  this  under  a  given/  constant  temperature  is 
what  gives  the  depth  of  carbon  desired,  and  by  the  proper  depth  of  the 
carbon  is  obtained  the  percentage  of  carbon  desired  in  the  surface  layer. 
The  percentage  of  carbon  in  a  carbonized  piece  of  steel  gradually  reduces 
from  the  outer  shell  to  the  core.  The  lower  the  carbonizing  temperature, 
the  less  the  time  of  submission  to  the  carbonizing  temperature,  and  the 
smaller  the  percentage  of  carbon  in  the  carbonizing  material  the  greater 
will  be  this  reduction. 

A  round  bar  of  steel  that  was  carbonized  to  the  depth  of  TG  of  an 
inch  was  examined  by  turning  off  A  of  an  inch,  and  analyzing  the  turn- 
ings for  carbon,  then  another  sixteenth  was  turned  off  and  analyzed,  and 
the  third  and  fourth  sixteenth  treated  in  a  like  manner.  This  gave  a 
carbon  content  of  1.24%  for  the  yV  of  an  inch  taken  from  the  outside,  the 
second  sixteenth  gave  0.85%  carbon,  the  third  sixteenth  showed  0.24% 
carbon,  and  the  fourth  or  core  contained  0.13%. 

The  time  of  submission  required  for  a  certain  depth  varies  with  the 
kind  of  carbonizing  materials  as  well  as  with  the  process  used.  The 
carbonizing  materials,  such  as  powdered  bone,  charcoal,  etc.,  which  require 
that  the  work  be  packed  in  an  iron  box  or  other  receptacle,  take  con- 
siderable more  time  to  carbonize  the  work  than  when  gases  are  used  to 


238  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

furnish  the  carbon,  owing  to  the  necessity  of  the  heat  penetrating  the 
box  and  carbonizing  materials  before  it  can  affect  the  work.  In  case  a 
deep  penetration  of  the  carbon  is  required,  and  the  carbon  in  the  car- 
bonizing materials  is  nearly  or  entirely  absorbed,  it  is  a  difficult  opera- 
tion to  insert  fresh  materials  in  the  packing  box. 

Another  point  might  be  mentioned  here,  and  that  is  that  all  steels 
do  not  retain  their  carbonization.  One  specimen  was  examined  by  taking 
a  very  thin  cut  from  the  outer  surface  for  a  part  of  its  length,  which  on 
analysis  showed  1.25%  of  carbon.  The  piece  was  then  laid  aside  for 
six  months,  and  a  similar  cut  taken  from  the  rest  of  its  length,  which  on 
analyzing  showed  only  0.92%  of  carbon.  This  showed  that  the  carbon 
dissolved  little  by  little  into  the  mass. 


CARBONIZING   WITH   GAS 

In  the  use  of  hydrocarbons,  or  gases,  a  fresh  supply  can  be  kept  flow- 
ing into  the  carbonizing  receptacle,  and  the  time  greatly  reduced  for 
deep  penetration  with  an  appreciable  reduction  of  time  for  the  shallow 
penetrations. 

A  very  important  factor  in  carbonizing  with  gas  is  the  furnace,  as 
on  the  design  and  operation  of  this  to  a  large  extent  depends  the  success 
or  failure  of  the  process.  They  are  designed  specially  for  this  purpose, 
and  are,  therefore,  not  practical  for  use  as  hardening,  annealing,  or  tem- 
pering furnaces,  although  they  might  be  made  useful  for  annealing  or 
hardening  large  quantities  of  work  by  being  fitted  with  appliances  for 
handling  the  same. 

This  makes  the  cost  of  installation  higher  than  for  the  appliances  used 
for  carbonizing  in  the  old  way.  The  cost  of  carbonizing,  however,  is 
about  one-half  of  that  of  the  old  method,  which  makes  the  furnace  soon 
pay  for  itself  by  the  saving  in  materials  and  labor.  Where  the  cost  of 
carbonizing  is  reduced  to  this  extent  it  makes  it  commercially  practical 
to  carbonize  steel  parts  that  were  considered  prohibitive  by  the  high 
cost  and  non-uniform  results  of  the  old  method.  Owing  to  the  nature 
of  the  process  of  carbonizing  by  the  old  methods  it  is  very  difficult  to 
obtain  uniform  results  with  pieces  packed  in  the  same  box,  or  to  repeat 
these  results  in  other  boxes. 

In  order  to  judge  the  temperature  of  the  pieces  packed  in  a  box  it 
is  necessary  to  insert  test  wires  through  the  cover.  After  a  certain  time 
a  test  wire  near  the  outer  edge  of  the  box  is  withdrawn  and  the  temper- 
ature is  found  to  be  just  right  for  carbonizing,  but  if  one  is  drawn  out  of 
the  center  of  the  box  at  the  same  time  it  will  be  seen  that  the  temperature 
here  has  not  risen  high  enough,  as  it  takes  a  much  longer  time  for  the 


CARBONIZING  239 

pieces  in  the  center  of  the  box  to  be  raised  to  the  proper  temperature 
than  for  those  near  the  outer  surfaces  of  the  box. 

As  the  carbonizing  material  must  be  packed  in  the  box  with  the  pieces, 
this  means  that  the  pieces  near  the  sides  of  the  box  will  begin  to  absorb 
the  carbon  before  those  in  the  center,  and,  therefore,  the  penetration 
will  be  greater.  As  the  percentage  of  carbon  in  the  outer  surface  of  the 
pieces  being  carbonized  is  greater  the  greater  the  depth  of  penetration, 
it  also  means  that  the  pieces  near  the  outside  of  the  box  will  have  a  greater 
carbon  content  on  their  surface  than  the  pieces  in  the  center,  and  this 
also  means  that  they  will  be  harder. 

Carbonizing  with  gas  overcomes  this  to  a  large  extent,  if  not  entirely, 
as  the  carbonizing  gas  is  not  turned  on  until  all  of  the  pieces  in  the  retort 
of  the  furnace  have  arrived  at  the  proper  carbonizing  temperature,  and 
it  is  shut  off  the  minute  the  proper  depth  of  carbonization  has  been  ob- 
tained. The  furnace  can  also  be  so  regulated  that  the  same  results  can 
be  obtained  with  the  next  lot  of  pieces  put  in  the  retort.  The  carbon 
in  the  retort  is  also  held  constant  by  the  steady  flow  of  the  gas,  and  the 
work  can  be  inspected  for  temperature  by  shutting  off  the  carbonizing 
gas  and  looking  through  the  outlet  pipe,  where  the  work  can  be  seen  and 
its  color  noted. 

A  special  furnace  for  the  gas  carbonizing  process  is  built  and  patented 
by  the  American  Gas  Furnace  Company,  and  is  shown  in  Figs.  138  and 
139.  In  Fig.  139,  A  is  the  retort  in  which  the  work  is  placed.  This  is 
made  out  of  extra  heavy  8-inch  pipe,  for  the  size  of  furnace  shown,  and 
is  made  to  revolve  on  the  rollers  B,  by  the  gear  wheel  C,  and  the  worm  D, 
which  in  turn  is  propelled  by  the  sprocket  wheel  shown  in  Fig.  138.  E  E 
are  air  compartments  to  prevent  the  heat  and  work  from  getting  into 
that  part  of  the  retort  which  extends  beyond  the  heating  furnace;  F 
is  the  heating-gas  chamber,  the  gas  coming  in  through  5  openings  or 
burners  similar  to  the  one  shown  at  G,  and  exhausting  out  through  others; 
H  is  the  cover  for  the  end  of  the  retort,  and  is  fastened  on  with  hinged 
bolts  and  thumb  screws.  This  is  taken  off  in  order  to  put  the  work  in 
the  retort,  the  partition  7  and  carbonizing  gas  outlet  J  coming  with  it. 

The  heating  gas  is  fed  through  pipes  and  burners  on  the  side,  and  the 
carbonizing  gas  passes  through  the  hose  shown  above  the  sprocket  wheel 
in  Fig.  138,  and  then  into  that  part  of  the  retort  where  the  work  is  held. 
After  the  carbon  has  penetrated  the  metal  the  gas  escapes  through  the 
outlet  /. 

In  this  process  the  carbonizing  gas  was  vaporized  from  the  liquids, 
naphtha  and  ammonia,  and  as  the  work  is  made  to  revolve  in  the  furnace, 
similar  to  the  action  obtained  by  a  tumbling  barrel,  an  even  depth  of 
carbon  is  obtained  on  all  sides  of  the  work,  and  this  overcomes,  to  a  large 
extent,  the  tendency  of  carbonized  pieces  to  have  hard  and  soft  spots, 


240 


COMPOSITION   AND   HEAT-TREATMENT  OF  STEEL 


as  the  soft  spots  are  usually  caused  by  the  piece  coming  in  contact  with 
something  that  would  not  allow  the  carbon  to  act  on  that  spot. 

Pyrometers  can  be  attached  to  the  furnace  to  gage  the  heat  for  the 
correct  temperatures,  and  when  this  has  been  attained  the  valves  and 


FIG.  138.  —  Revolving  retort  furnace  for  carbonizing  with  gas. 


cocks  can  be  set  so  that  the  work  can  be  duplicated  for  any  number  of 
times  and  the  furnace  run  for  a  long  period  with  an  assurance  of  the  quality 
of  the  work  turned  out,  as  the  temperature  is  held  constant.  Starting 
with  a  cold  furnace  in  the  morning,  an  hour  and  a  half  is  usually  required 
to  get  the  work  hot  enough  to  absorb  the  carbon. 

Odd-shaped  and  intricate  pieces  can  be  carbonized  by  this  method 


CARBONIZING 


241 


1 

I" 

-• 

J 

i 
I 

! 
1 

i 

,. 

a 

\ 

242 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


CARBONIZING 


243 


that  it  would  be  difficult  to  do  by  packing  in  an  iron  box  in  such  materials 
as  bone  and  charcoal.  This  is  best  illustrated  by  the  piece  shown  in  Fig. 
140  that  has  been  broken  open  to  show  the  action  of  the  carbonizing  gas 
on  the  seven  small  holes  around  its  rim,  and  it  will  be  seen  by  a»  glance 
at  the  half-tone  that  the  carbon  penetrated  to  a  good  depth  all  around 
these  holes.  The  piece  to  the  left  shows  the  surface  that  was  broken 
at  a  distance  of  about  4  inches  from  the  end  to  the  right.  It  also  showed 
that  the  carbon  had  a  good  even  penetration  as  to  depth  on  all  of  its 
exposed  surfaces  both  inside  and  outside. 

The  results  of  different  lengths  of  time  that  the  work  is  submitted  to 
carbonization  in  this  gas  furnace  is  shown  in  Figs.  140  and  141.  The 
distinct  line  between  the  carbonized  shell  and  the  core  is  obtained  by 
plunging  the  metal  directly  from  the  carbonizing  furnace  into  a  quench- 
ing bath.  By  Fig.  141  is  shown  the  depth  of  carbon  that  is  obtained  in 


FIG.  141.  —  Quenched  directly  from  the  carbonizing  furnace. 

this  furnace  by  carbonizing  for  4,  8,  10,  12,  14,  and  16  hours,  and  then 
quenching  in  a  lard-oil  bath  directly  from  the  furnace.  The  test  bars 
were  f  inch  in  diameter,  and  are  reproduced  here  at  about  their  actual 
size.  The  results  as  to  depths  for  this  set  of  pieces  is  as  follows: 


Time  for  Carbonizing  in  Hours 


4 
8 
10 
12 
14 
16 


Depth  of  Penetration  in  Inches 


0.040 

0.062 
0.071 
0.079 
0.085 
0.090 


The  set  of  test  pieces  in  Fig.  142  shows  the  depth  of  penetration  for 


244 


COMPOSITION   AND   HEAT-TREATMENT   OF   STEEL 


CARBONIZING 


245 


each  hour,  from  1  to  9  inclusive,  as  follows,  as  well  as  the  size  and  shape 
of  the  piece: 


Time,  Hours 

Size  of  Test  Piece 

Depth  in  Inches 

1 

I  in.  round 

.015 

2 

I  in.  round 

.020 

3 

f  in.  round 

.030 

4 

I  in.  round 

.038 

5 

\  in.  round 

.046 

6 

\  in.  round 

.053 

7 

\  in.  round 

.056 

8 

\  in.  round 

.058 

9 

\  in.  round 

.060 

9 

\  in.  round 

.063 

9 

i  in.  square 

.075 

— 20H- 


MM 

Soft 

"f" 


f 

;1  a 

§£ 

Hard 

a 

| 

Rad. 


FIG.  143.  —  Samples  of  local  hardening  by  carbonizing. 

Intricate  or  peculiar-shaped  pieces  that  would  not  turn  over  in  the 
furnace,  but  slide  around  on  the  bottom,  would  have  very  little  carbon 
on  the  side  that  remained  in  contact  with  the  retort.  For  these  it  would 
be  necessary  to  put  something  inside  of  the  furnace  so  constructed  that 
it  would  cause  them  to  turn  over.  Delicate  pieces  that  would  be  liable 
to  break  would  also  have  to  have  some  special  apparatus  inside  of  the 
retort  to  protect  them. 


246  COMPOSITION  AND  HEAT-TREATMENT  OF  STEEL 

LO.CAL    HARDENING 

The  carbonizing  process  is  often  used  for  hardening  certain  parts  of 
a  piece,  and  leaving  the  rest  soft,  as  illustrated  by  the  pieces  shown  in 
Fig.  143.  The  three  pieces  are  turned  from  machinery  steel  to  the  lines 
shown  by  the  outside  line  of  each  piece.  After  this  they  are  carbonized 
to  the  proper  depth,  then  annealed,  and  then  the  parts  shown  by  the 
sectional  lines  are  turned  off,  after  which  they  are  hardened. 

By  turning  off  the  parts  shown  by  the  sectional  lines,  the  outside  layer 
that  has  been  carbonized  is  turned  off,  and  this  leaves  these  parts  with 
the  machinery  steel  exposed.  When  hardening,  therefore,  the  machinery 
steel  does  not  harden,  and  consequently  remains  soft,  while  the  balance 
of  the  pieces,  which  have  a  carbonized  outer  shell,  do  harden,  and  this 
makes  the  pieces  hard  in  the  parts  desired  and  soft  in  the  other  places. 


INDEX 


Acetylene,  147,  231,  233. 
Acid  Bessemer  process,  17. 

hydrofluoric,  193,  195. 

open-hearth  process,  27,  29. 

picric,  193,  197. 

sulphuric,  200. 
Alkali,  chlorides,  236. 
Alkaline  cyanides,  231. 
Alkaline  earths,  236. 
Alpha  iron,  68. 

Aluminum,  75,  76,  83,  86,  88,  107, 
118,  123,  144,  230. 

granular,  86. 
Ammonia,  231,  232,  233,  234. 

nitrate  of,  195. 
Animal  black,  231,  232,  234. 
Annealing,  185-191. 

cast-iron  box  for,  188. 

furnaces,  190. 

Howe's  laws,  188,  189. 

laws  of,  186. 

materials,  190. 

rules  for,  187. 

temperature  effects,  189. 
Anthracite,  231,  233. 
Antimonides,  89. 
Antimony,  78,  88,  89,  90,  175. 
Apatite,  79. 

Area,  reduction  of,  187,  214,  220. 
Arsenic,  42,  78,  88,  89,  90. 
Arsenides,  89. 

Austenite,     66,     195,     199,     209, 
215. 

Barium,  232. 

carbonate,  231,  234. 

chloride,  175. 

Basic  open-hearth  process,  27,  30. 
Baths,   barium  chloride,    175. 

hardening,  199,  204. 

lead,  221-223. 

oil,  223-225. 

salt,  225-226. 

tempering,  221-226. 


Bessemer  process,  1,  6,  13. 

Beta  iron,  68. 

Bichromate  of  potash,  232,  234,  235. 

of  potassium,  231. 
Billets,  19. 

Bismuth,  78,  88,  89,  90. 
Blast  furnace,  1-12. 

combined  electric  and,  10-12. 
Blooms,  19. 

Blow-holes,  14,  30,  31,  72,  75,  76,  83,  106, 
109,  107,  108,  117,  120. 

Bone,  228,  231,  232,  237. 
Borate  of  lime,  91. 
Borax,  93. 
Boric  acid,  91. 
Boron,  91. 
Braunite,  71. 
Briquettes,  ore,  12. 
Brittleness,  237. 

Calcium,  75. 
Campbell  process,  32. 
Carbide  of  iron,  74,  193. 
Carbon,  9,  10,  12,  13,  22,  29,  33,  34,  39, 
45,  50,  64,  65,  66,  67,  69,  70,  71,  74, 
76,  79,  80,  82,  86,  87,  88,  116,   118, 
119,  123,  124,  126,  144,  152,  193,  195, 
198,  199,  201,  216,  227,  229,  230,  231, 
232,  236,  237,  238. 
combined,  1,  4,  193. 
content,  68. 

214-          dissolved,  193. 
graphitic,  1,  4. 
speed  of  penetration  of,  228. 
Carbonate,  71. 

of  barium,  231,  234. 
of  lime,  200. 
of  magnesia,  200. 
Carbonic  oxide,  75,  232. 
Carbonizing,  227-246. 

depth   of,   penetration  in,  230,   233, 

234,  235,  243-245. 
effects  of  elements  in,  230. 
electrical,  228. 
247 


248 


INDEX 


Carbonizing,  factors  governing,  228-231. 

furnace,  239. 

gas  process  of,  238-245. 

Harveyizing  process,  227. 

heat  treatment  after,  236. 

Krupp  process,  228. 

local,  246. 

materials,  231-235. 

rates  of  penetration  in,  234,  235,  243- 
245. 

temperature  effect  on,  236. 

time  of  exposure,  237. 
Carbon  monoxide,  13,  83,  231,  233. 
Case-hardening  (see  Carbonizing),  227-246. 
Casting,  116. 
Castings,  1. 

direct-steel,  121. 

gray  iron,  6. 

steel,  27. 

steel,  properties  of,  118. 

Tropenas  process,  117. 
Cast  iron,  18. 
Cementation  process,  65. 
Cementite,  66,  79,  193,  194,  195,  196,  197. 
Cerium,  110. 
Charcoal,  9,  12,  31,  65,  190,  227,  231,  232, 

234,  235,  237. 
Charred  bone,  190. 

leather,  190. 

sugar,  231,  232,  234. 
Chloride  of  barium,  175. 

of  alkali,  236. 
Chrome-nickel,  100. 

-vanadium,  100. 

Chromium,  36,  50,  60,  69,  74,  93,  99,  102, 
122,  123,  124,  208,  228,  229,  230,  231. 

oxide,  232. 
Cobalt,  97,  98. 
Cohesive  force,  205. 
Coke,  1,  4,  12,  17,  31,  233. 
Compression,  limit  of,  186. 
Conductivity,  200,  201. 
Converter,  Bessemer,  13,  14,  17. 
Copper,  42,  75,  86,  87,  88. 
Copper  sulphide,  87. 
Corrosion,  28,  85,  88. 
Cracking,  205-208,  236. 
Critical  temperatures,  193,  199.    See  also 
Recalescent,  Decalescent,  and  Trans- 
formation points. 
Crucible  process,  1,  6,  34. 


Crucibles,  fire-clay,  34. 

graphite,  34. 

Crystalline  structure,   114. 
Crystallization,  237. 

of  annealing,  187. 
Cupola,  spiegel,  15. 
Cupro-titanium,  108. 
Cyanate{   232. 

of  potassium,  232. 
Cyanide,  178,  236. 

alkaline,  231. 

ferro-,  231,  232. 

of  ammonia,  232. 

of  potassium,  175,  231,  232,  236. 
Cyanogen,  232. 

Decalescent  points,  68. 
Decarbonization,   27. 
Deflection,  218,  219. 
Dolomite,  17. 
burned,  30. 
Dynamics,    197. 
Dynamic  properties,  229. 

Elastic  limit,  189,  192,  198,  199,  201,  214, 

215,  218-219,  220. 
Electric  blast  furnace,  8-12. 
Electric  current  for  iron  furnaces,  11. 
Electric  furnaces,  see  Furnaces,  electric. 
Electric  process,  1,  6. 

welding,  145-147. 
Electrical  conductivity,  193. 
Electrodes,  9,  11,  12. 
Elongation,  189,  198,  199,  201,  214,  215, 

220. 

Erosion,  195. 
Eiitectic  steel,  67. 
Ferrite,  66,  87,  92,  116,  193,  194,  195,  196, 

197. 

Ferro-aluminum  silicon,  60. 
-boron,  91. 
-chromium,  99. 
-cyanide,  36. 

-cyanide  of  potash,  232,  234,  235. 
-manganese,  29,  31,  36,  71,  84,  85,  107, 

108. 

-mangano-aluminum-silicon,  60. 
-mangano-silicon,  61. 
-silicon,  29,  75,  76,  77,  78,  86,  108. 
-silicon-manganese,  71,  75. 


INDEX 


249 


Ferro-titanium,  18,  19,  105,  107,  120. 

vanadium,  120. 
Ferrous-titanate,  105. 
Fiber  stress,  219. 
Fire-clay,  190. 
Fluorspar,  86. 
Fluxes,  45. 
Flux,  magnetic,  50. 
Forging,  122-124. 

drop-hammer,  131-135. 

hand,  126. 

press,  136-143. 

steam-hammer,  127. 

temperatures,  124-125. 
Fuels,  furnace,  153-181. 

crude  oil,  155. 

gaseous,  163. 

hard,  153. 

kerosene,  154. 

liquid,  154. 

producer  gas,  163. 
Furnace,  electric,  Colby,  49. 

Girod,  56. 

Heroult,  45. 

Keller,  47. 

Kjellin,  49. 

refining,  40. 

Stassano,  42. 

Richling-Rodenhauser,  53. 

Combined  gas  and  electric,  63. 
Furnaces,  blast,  1-12. 

carbonizing,  239-245. 

combined  electric  and  blast,  10-12. 

electric,  42-57. 

electric  smelting,  8-12. 

hardening,  210-213. 

heat  treatment,  151-184. 

barium-chloride  bath,  178. 

cyanide  of  potassium  bath,  175. 

electric,  182-184. 

gaseous  fuel,  163-181. 

temperature  regulator  for,  170. 

hard  fuel,  153. 

lead  bath,  175. 

liquid  fuel,  154-163. 

liquid  heating,  174-181. 

Gamma  iron,  68. 

Gases,   carbonizing,   228,   231,   232,   233, 

234,  238-245. 
illuminating,  231,  233. 


Gases,  occluded,  18,  19,  30,  77,  83,  104. 
Gasoline,  231. 
Graphite,  66,  194,  231. 

Hammer,  hardness,  187. 

hard  steel,  186. 

steel,  38. 
Hardening,  192-213. 

baths,  199-204. 

carbon  effects  in,  198. 

cracking  in,  205. 

effects  of,  199. 

electrical,  204. 

factors  in,  193. 

furnaces,  210-213. 

high-speed  steels,  208. 

mechanical  effects  of,  198. 

preheating  in,  207. 

temperatures,  effects  of,  200. 

warping  in,  206. 
Hardenite,  195-197. 
Hardness,  192,  215,  227. 
Harveyizing,  65. 
Hematite,  62. 
Horn,  231. 

Hot-blast  stoves,  1-4. 
Hydrocarbon,  83,  232,  236. 
Hydrofluoric  acid,  193,  195. 
Hydrogen,  66,  83,  84,  85,  149. 

Illuminating  gas,  231,  233. 

Impact,  218. 

Ingots,  16. 

Internal  strains,  185,  205,  214. 

Iodine,  tincture  of,  193,  197. 

Iridium,  94. 

Iron,  blast-furnace,  16. 

carbide,  193. 

cast,  18. 

ore,  1,  4. 

oxide  of,  28,  29,  215,  232. 

phosphide  of,  73. 

pig,  1,  9,  10,  12,  13,  30. 

wrought,  30,  36,  37,  40. 

Krupp  process,  66. 

Ladle  cars,  hot  metal,  5. 
Lanthanum,  110. 
Lash  mixture,  61. 
process,  61. 


250 


INDEX 


Lead  bath,  221. 

-tin  baths,  221-223. 
Leather,  charred,  231,  234. 
Lime,  carbonate  of,  200. 

slacked,  190. 
Limestone,  1,  4,  17,  25,  28,  30,  86. 

burnt,  56. 

Machinery  steel,  68. 
Magnesia,  17,  190. 

carbonate  of,  200. 
Magnesite,  30,  47. 
Magnesium,  150. 

oxides,  79. 
Magnetic,  193. 

qualities,  192. 
Magnetite,  61. 

Manganese,  1,  13,  14,  15,  29,  31,  32,  36, 
38,  39,  40,  50,  63,  65,  69,  71,  72,  73, 
74,  75,  76,  77,  80,  83,  85,  86,  88,  101, 
102,  116,  118,  119,  121,  122,  123, 
124,  126,  198,  201,  228,  230,  231. 
Manganese,  ferro-,  29,  36,  71,  73. 

oxide,  29,  30,  73,  231. 

silicate,  82. 

sulphide,  14,  19,  73,  81,  85. 
Manganite,  71. 
Martensite,  110,  195,  196,  197,  198,  199, 

206,  207,  229. 
Martin  process,  22. 
Mercury,  200,  202. 
Methane,  233. 
Mica,  190. 

Microscopical  examination,  193-197. 
Mill,  slabbing,  19,  111. 

tilting  table,  111. 
Molds,  ingot,  16. 
Molybdenum,  102,  103,  208,  230. 
Monell  process,  32. 
Monel  metal,  95. 

Naphtha,  231. 

Nickel,  34,  42,  50,  60,  74,  93,  95,  96,  97, 

99,  120,  123,  144,  228,  229,  230. 
chrome,  42,  236. 
Nitrate  of  ammonia,  195. 

of  potassium,  200. 
Nitrogen,  83,  84,  104,  105,  106,  107,  117, 

118,  231,  233-34. 
Non-magnetic,  185,  193. 


Oil  baths,  223-225. 
Open-hearth  process,  1,  13,  22. 

acid,  1,  6. 

basic,  1,  6. 
Ore,  17. 

briquettes,  12. 
Overheating,  152. 
Oxidation,  28. 
Oxide,  210. 

carbonic,  232. 

chromium,  232. 

magnesium,  79. 

manganese,  198. 

of  iron,  28,  215,  232. 

scale,  210. 
Oxidizing,  188. 
Oxy-acetylene,  147. 

Oxygen,  1,  13,  19,  29,  30,  40,  45,  73,  76, 
83,   84,   85,   86,   117,   118,   119,  147, 
176,  190,  210. 
Oxy-hydrogen,  149. 

Pearlite,  66,  87,  92,  110,  194,  195,  215,  229. 

of,  228. 

Petroleum  gas,  231. 
Permanent  set,  218-219. 
Phosphate  of  lime,  79. 
Phosphide  of  iron,  73. 
Phosphides,  78,  89. 

Phosphorus,  1,  13,  17,  18,  19,  28,  29,  30, 
31,  32,  38,  40,  42,  46,  47,  56,  63,  65, 
74,  77,  78,  79,  80,  81,  85,  88,  117, 
118,  124,  126,  198,  201. 
Picric  acid,  193,  197. 
Pig-casting  machines,  7,  8,  9. 

iron,  9,  10,  12. 
Pigs,  1,  4,  6,  8. 
Platinum,  94. 
Potash,  bichromate  of,  232,  234,  235. 

ferro-cyanide  of,  232,  234,  235. 

prussiate  of,  231. 
Potassium,  36,  75. 

cyanate,  232. 

cyanide,  231,  232,  236. 

ferro-cyanide,  231,  232. 

nitrate,  200. 

Prussiate  of  potash,  231. 
Pyrometers,  164. 

Quenching  baths,  199-204. 


Occluded  gases,  18,  19,  30,  77,  83,  104.  Rails,  steel,  17. 


INDEX 


251 


Rails,  steel,  sulphur  in,  19. 

Recalescent  points,  67,  185,  192,  193,  199. 

See  also  Critical  and  Transformation 

points. 

Recarburized,  22. 
Recarburizing,  15,  31. 
"  Red-hardness,"  209. 
Reduction  of  area,  187,  214,  220. 
Refractory  earth,  190. 
Rolling,  111-114. 
rules  for,  115. 
temperatures,  116. 
Rolls,  slabbing,  111. 

Sal  ammoniac,  200. 
Salt,  36,  200. 

baths,  225-226. 
Sand  annealing,  190. 

silica,  6. 

tempering,  226. 
Sawdust,  190. 
Scaling,  188. 
Scrap,  steel,  28. 
Shock  resistance,  192,  199,  215,  218,  227, 

229. 

Silica,  29,  30,  74. 
Silicates  of  iron,  75. 
Silicide,  75. 
Silicious  materials,  29. 
Silicon,  1,  14,  16,  17,  29,  30,  31,  34,  37,  38, 
39,  40,  63,  65,  71,  75,  76,  77,  78,  80, 
83,  85,  86,  94,  116,  118,  119,  123,  124, 
126,  198,  201,  230. 

dioxide,  75. 

-ferro,  29,  75,  76,  77,  78. 

ferro-manganese,  71. 

in  electric  furnace,  77. 

in  iron,  12,  13 . 

oxidation  of,  29. 

results  on  quenching,  76. 

spiegel,  76. 
Slag,  10, 16, 19, 25, 27, 29, 30, 40, 56, 76, 119. 

lime-iron-oxide,  60. 

oxidizing,  79. 
Slig,  12. 
Sodium,  75. 

Sorbite,  189,  195,  197,  206. 
Sows,  4,  6,  8. 

Specific  heat,  200,  201,  202. 
Spiegeleisen,  15. 
Spontaneous  annealing,  187. 


Static  strength,  197,  214. 

Stove,  hot-blast,  1-4. 

Strains,  internal,  185,  205,  214. 

vibrational,  218. 
Stress,  fiber,  219. 
Sugar,  charred,  231,  232,  234. 
Sulphide  of  iron,  81. 

of  manganese,  81. 

Sulphur,  1,  13,  18,  19,  28,  29,  30,  31,  32, 
38,  40,  42,  46,  47,  56,  63,  65,  73,  74, 
80,  81,  82,  83,  84,  85,  86, 117, 118, 119, 
124,  126,  190,  198. 
Sulphur  in  coke,  12. 

in  electric-furnace  iron,  12. 
Sulphuric  acid,  200. 

Talbot  process,  22. 
Tantalum,  93. 
Tempering,  186,  214-226. 

colors,  216. 

crank-shafts,  218. 

effects  of,  220. 

furnaces,  220-226. 

gears,  218. 

sand  process,  226. 

springs,  217. 

temperatures,  215-216. 
Tempering  furnaces,  gas,  220. 

electrically  heated,  224. 

lead  bath,  221. 

oil,  220,  223. 

salt  bath,  225. 
Tensile  strength,  29,  186,  187,  189,  192, 

198,  199,  201,  214,  215,  220. 
Tincture  of  iodine,  193,  197. 
Titaniferous  ores,  105. 
Titanium,  18,  19,  84,  86,  105,  108,  120, 

123,  228,  229,  230. 
Titanium-,  cupro-,  108. 
Titanium,  ferro-,  18,  19,  120. 
Tool  steel,  68. 
Torsion,  218. 

Transformation  point,  185,  186,  187,  188, 
189,  190,   192,  193,  197,  199,  208-209 
214,  237.     See  also  Recalescent,  De- 
calescent,  and  Critical  Points. 
Troostite,  197,  206. 
Tropenas  process  of  casting,  117. 
Tungstates,  101. 

Tungsten,  34,  42,  50,  60,  69,  100,  101,  102, 
123,  124,  208,  230. 


252 

Tuyeres,  4,  12. 
Uranium,  103. 

Vanadium,  84,  86,  99,  103,  104,  105,  119, 
120,  123,  144,  228,  229,  230,  231. 

chrome,  34,  105. 

ferro-,  120. 

Vibrational  strains,  218. 
Viscosity,  200,  201. 


INDEX 

Volatility,  200,  201. 


Warping,  205-208,  236. 
Welding,  143-145. 

electric,  145-147. 

oxy-acetylene,  147. 

Thermit,  149-150. 

with  gases,  147-149. 
Wolframite,  101. 


Of  THE 

UNIVERSITY 

Of 
I  Ll  FOR  Wj 


YC  34068 


